Shift the chain onto the smallest rear cog and smallest front chainring if possible
Open the rear derailleur by pushing it forward to create slack
Place the chain on the front chainring first
Guide the chain onto the top of the rear cog
Rotate the pedals forward slowly by hand to pull the chain into place
If the chain is off the chainring, lift it onto the teeth while turning the crank slightly
If the chain is stuck between gears, move the derailleur cage and free the chain carefully
Check that the chain is seated on the front chainring, rear cog, and derailleur pulleys
Pedal forward by hand several full rotations to confirm it runs smoothly
If the chain keeps slipping off, inspect for a bent derailleur, damaged chain, or misaligned gears