Besides the rounded spreaders that I made to create the epoxy fillets and I also made some sharp knife like scraping tools for cleaning up the edges of the fillets as I created them.
You can also buy pre-made epoxy fillet tools from West System and some other companies. I find the wood ones to be nice though because I just wipe them off, and then after the epoxy hardens up I run them over the belt sander quickly to refinish them.