It can be done. Clean the floor free of any soils, dirt and debris. Scuff sand it with a 60-80 grit paper to create a texture that the coating can mechanically bond to. Remove the debris prior to application. This can be cleaned with soap and water or a solvent reducer, tack ragged or vacuumed. Don't leave any residue on the surface. Just remember that whatever is applied over it will be relying on the existing coatings adhesion to the floor. It's only as good as that. If its loose or failing, I'd remove it prior to coating again.
Hope this helps.