Found this online
Method #2: Thinning Epoxy Resin Using a Solvent
Using a solvent to thin your epoxy is a much easier and quicker method, but it will drastically affect the compressive strength of the epoxy, so we do not recommend this method. However, if you still go ahead with this, here are some of the solvents we suggest you use. Solvents like denatured alcohol, lacquer thinners and acetone.
It also said heating to thin is probably best but not to over heat it.