Can you touch up epoxy garage floor paint?
I called up Rustoleum to ask about their EpoxyShield product since that's what was used previously.

They informed me that the epoxy coating needs to be reapplied every 3-5 years (which is about how old the current coating is.)

Recommendation was to scuff sand existing epoxy coating with 60 grit sand paper over the entire surface to aid with adhesion, clean, allow to dry and recoat.

Basically, just treat it like painting over any other type of glossy paint.