Trex is a wood composite material that doesn't need paint to protect it from the Sun or from absorbing rain water.

If you painted with a latex paint, then that paint is too soft to provide good service on a working surface such as a step. Just use the steps normally, and the paint should wear off on it's own. (It'll likely get very dirty looking because dirt will become embedded in it underfoot. If you get fed up with it, I expect that any paint stripper would take latex paint off of Trex without harming the Trex, but test in an inconspicuous area first.

Rejoice, Higgs. What you did was acquire "experience". Now, if anyone ever asks you if they should paint their Trex decking, you have all the experience needed to answer their question with both confidence and authority, having done that once yourself.

If you get tired of the way that paint looks, take it off with a paint stripper. Just check that the paint stripper doesn't affect the Trex by testing it in an inconspicuous area.