I founded a solution.
Settings - general - mobile devices, at this place I deleted all mobile devices including Android because android app made folder "protected" because it was used for scheduling. So now with uninstaled outlook app and device removed, folder is not any more protected and it was deletet with ease....
On Android built in app and on online outlook falder isnt there any more :) just make shure to outlook android app dont make other folder "protected" (used for scheduling mails). If You use that option again, problem will be there again.