after i add effects to several tracks, how do i remove an effect i added to a previous track?
Audacity has unlimited (subject to available hard disk space) levels of “Undo”.
So basically, you can undo it, but not AFTER you’ve applied other effects, b/c you’ll have to undo all THOSE to get to the one you’re trying to get rid of.
In short, make sure you like an effect before moving on to others.