Do you know where to find Middle C on a piano?
If so, on a 4-string bass, that note is G-string/17th fret.
Go to Middle C...go down 3 octaves...move down a 1/2 step(to "B"). It's early here; I think that would be the low "B" of a 5-string.
Do you have both instruments in the same room?
The Acoustic bass is tuned the same as a 4-string electric bass(E-A-D-G).
Recall that Bass is played an octave LOWER than written.
(Otherwise, there would be many ledger lines below the staff).