You my submit a bug or you may submit in game via the Customer Service Button located in game. If you do not know how to submit a report here is a nifty how to guide below.
To submit a report please fill out the following information:
-Steps to replicate bug
-Buffs and items on character
-Type of phone (Android, Apple, Operating system etc.)
Please include any screenshots or videos you may have taken to document the report.