If Step 2 is not enough, push rear derailleur forward to release tension on the chain.

Lift the chain and put it back on the chain ring.

Turn the pedals with your hand while lifting the rear wheel to realign the chain (as in Step 2).

Bike chains are very greasy and your hands will get messy. Use a pair of latex gloves, if available, or use a twig or leaf if you can.

This step may take several attempts, but it will work eventually.