Empty the cooler and thoroughly clean out the inside with warm water and several drops of dish soap. Dry the cooler out with a towel afterward. It must be completely clean for a repair to be effective.
Sand the bottom of the cooler down with course fine-grit sandpaper to help roughen the surface so it bonds more effectively with the repair.
Apply an epoxy repair putty to the cooler floor with a putty knife. Use the putty knife to smooth it out as much as possible and let it harden overnight.
Place a liner over the cooler floor to protect it against future damage.
Fill the cooler partially with water to test it so you know the cooler won't leak and is working optimally.