Why is 1 of the 4 propellers not spinning as well as the other 3?

i was flying my drone and it hit a wall, it still flew after that like normal. i put it away and when i checked it again 3 of rotors were spinning as normal and 1 wasn't. there was something stuck around the motor which i removed. it started to move slightly but as much as the other roters.

how do i fix it