Ultimately - it's a matter of time spent focusing on different aspects of the instrument. Guidance speeds it up but the initial hurdle of just about any technique will make you think your hands must be mentally challenged.
I spent at least a month just plucking open strings for 20-30 minutes a day when I gave up guitar for bass to develop my plucking hand technique - starting slowly and building it up. Played some Rocksmith to give me something to attempt to play which helped. Spend 5-10 minutes plucking fingers, another 5-10 on exercises in the links below, spend 5-10 minutes learning scales and chord shapes starting with the major scale in the key of C, spend 5-10 minutes noodling - i.e. trying to make music out of the notes within the scales you know. Spend another 10-20 minutes learning any songs you want to learn by ear and/or with notation or tablature . Spread it out through out the day, do it all in 30 minutes to an hour, just take a stab at it every day. Break it up and focus on one aspect at a time, then try to make it all work together.
Learning some scales and chord shapes helps but check out this link -
https://www.guitarplayer.com/technique/warm-up-time-11-exercises-that-will-help-you-play-even-better
Specifically figures 1-4. These aren't musical scores so any pattern covering 4 strings can be applied to the bass.
use the tab - the bottom line is the lowest string the top line is the highest, the number is which fret to play. if it says run 5 6 7 8 index on the 5th fret, middle on the 6th fret, ring for the 7th, pinky for the 8th. Then shift up for the next 4 frets.
ignore any exercise using chords unless you also want to play guitar.. but figures 1-4 can be applied to your fretting hand on the bass, minus the high B and E strings. You can probably find something similar like this specifically for bass if you google, but it's pretty much the same concept.
Do them once a day for a couple weeks, start from the 5th fret early on and over time work your way to the 12th fret, once you can do that then start from the first fret to develop your reach across the fretboard and the stretching will strengthen and make your fingers more flexible.
These are also great exercises as a warm-up throughout the future to help loosen you up and get your blood flowing before a session or a show. Start slow - 60 BPM and work your way up 2-5bpm at a time. You don't HAVE to use a metronome but might as well start developing your timing. Weeks to months later you'll be able to handle it at faster tempos to a click or a drum beat if you regularly incorporate both.
While you're at it - there's a book called bass aerobics that will start you out with exercises to help you develop your plucking hand with emphasis on alternating while ascending, and raking while descending if using finger technique.
Here's a video from a different person - Scott Devine - who will show you what is meant by alternating and raking.
- Take any free education you can find.. seek a local bass instructor (preferably a bass instructor not a guitarist who teaches bass)
Most importantly, be patient. Music is something one never stops learning if they pursue it in their lifetime. It doesn't happen overnight. It takes work and the sooner you begin, and the more you do with some guidance on proper techniques, and some theory doesn't hurt the better you'll get over the years.
You can also build individual finger coordination a bit without an instrument near by. It doesn't really help with fretboard familiarization but it does help get your fingers used to moving by themselves.
Just place your hand flat on a table or desk or your bed and practice lifting one finger at a time. The hand I fret with does this a lot easier than my right, as I tend to only use two fingers on the right.
There are also hand exercise machines designed to exercise fingers individually.
so I tried to find a photo of a successful famous pro who has a long middle finger like you. Here is a photo of Daryl Jones from the Rolling Stones. Notice that he has a long middle finger and, like you, he needs to curve his middle finger, or else it is too long to reach the E string. The important difference, though, is notice how his wrist is lower than your wrist. This allows him to straighten his hand and uncurl his 3rd and 4th fingers, so that all four of his fingers are roughly parallel and pointed up at the ceiling. If you compare his left hand with your left hand, do you agree his hand looks more relaxed and neutral than yours?
