Easy!!

Mix a good amount of epoxy. i usually go for about 1oz total. then add a few drops, only a few!! 2 or 3 drop max of Methyl Hydrate / denatured alcohol to the mix. and mix.

It should thin. do not use more than a few drops, as it'll weaken / break down teh epoxy, and increase cure time. if you use too much, the epoxy might take days to fully cure, and even then, it'll be spongy, like a sponge (full of holes too!!)

Nother metod it to warm teh epoxy when you mix it/ warming it makes it runnier, but eh cure time decreases. Put your mixing cup in a mug of hot water, and mix. the heatr should really thin it up.

Also, you can paint on teh epoxy, then blast it with your heat gun. that shoudl also make it run, and flow into all teh little nooks and crannies!