There's a floating widget that can't be moved, appeared on my phone. How can I remove it?

[AC Question]

There's a floating widget that can't be moved, appeared on my phone. How can I remove it? It looks like a green circle with a fan and if you touch it, the fan starts spinning and after several seconds it would say "Successfully Released ... MB"

 

[lucianus_luciferus]

it is probably a cleaner app you have installed