I usually just type out my app name in a bespoke font from any of these and screenshot and crop it to a square and call it a logo. But sometimes it may not cut it. These might help you
- UCraft free logo maker
 - Canva - aint nothing like good ol canva.
 
I usually just type out my app name in a bespoke font from any of these and screenshot and crop it to a square and call it a logo. But sometimes it may not cut it. These might help you