Try to think about your whole hand at once. The goal here is to relax as much as possible. Obviously, you have to use some muscles to actually push the string, but to use them no more than necessary—AND also not to use any muscles that aren't necessary.
As a violin teacher, when I see tension in a student's left hand, the thumb is often part of it; they're clenching their entire hand into a fist. I ask them to tap their thumb against the neck a few times. This does a few things: it focuses their attention on a part of their hand they weren't thinking about, but also, to "tap," you have to first release the pressure to move the finger away; after the tap they can replace the finger with a relaxed contact.
Try reminding yourself to do this; at random times while playing, tap your thumb; if any fingers are on strings but are not the "front fingers" (e.g. if one finger is on fret 5 but another is resting behind it on fret 4, not changing the pitch) then tap those. Try to consciously relax your entire hand (and arm!).
See also this answer, and its question about where to press the string. The answer makes the good point that you only need to press until the string meets the fret, not the wood.