[yortem]

my friend downloaded app that blocked him from donig a lot of stuff in his phone, including access to app manager.
how can he delete that app? maybe from folder? what can he do?

[Mooncatt]

Try booting the phone into safe mode, which doesn't start third party apps. Then he should have access to his app manager. You'll want to either Google how to do this or post the phone model here so someone can give specific instructions. There are multiple ways to boot into safe mode depending on the phone and I'm not familiar with all of them.

If this app was downloaded from a place like Google Play, he could also try going to the app's page and uninstalling from there.