If the relief is high, then the strings are pulling more that the truss rod. So the truss rod needs to tighten, not loosen.
To check the relief, hold the first fret (so you eliminate the nut being the factor), and hold the fret where the necks joins the body. You can also put a capo on the first fret if you have one, directly on the fret, to free up a hand.
The string acts as a straight edge, and you are looking to see a little daylight between the string and the fret that is halfway between the two frets you are holding. It varies by how much, but the thickness of a credit card is ball park.
Tighten a little, play it, then revisit
If you are getting no movement, of the truss rod is moving too freely or not at all, take it to a tech
To check the relief, hold the first fret (so you eliminate the nut being the factor), and hold the fret where the necks joins the body. You can also put a capo on the first fret if you have one, directly on the fret, to free up a hand.
The string acts as a straight edge, and you are looking to see a little daylight between the string and the fret that is halfway between the two frets you are holding. It varies by how much, but the thickness of a credit card is ball park.
Tighten a little, play it, then revisit
If you are getting no movement, of the truss rod is moving too freely or not at all, take it to a tech