My 2 wheeled bike chain fell off,I'm trying to fix it but its to hard.The hard part is my bike has a cover on the circle to put the chain on.And i gotta put the bike back and its just to hard the chain keeps falling off and stuff.Tell me how to fix a bike chain that has a COVER on the circle thing to put the bike chain!Help me like get a video that has as cover on the thing..please help.