How to Put a Mountain Bike Chain Back On: A Step-by-Step Guide
To put a mountain bike chain back on, first, shift the chain to the smallest cog in the rear and the smallest chainring in the front. Then, loosen the rear derailleur or derailleur hanger so the chain has enough slack to fit back on the cassette and chainring. Next, place the chain back onto the cassette and chainring, making sure it is seated correctly. Finally, pull the rear derailleur back into position and tighten it so the chain is taut and ready to ride.