If you experience a lot of slipped chains, your chain might be too long. In this case, you will need to use a chain breaker.

Put the chain on the outer chain guide of the chain breaker.

Turn the handle on the chain breaker to push the chain pin part of the way out.

This step may take quite a bit of force so don't be afraid that you are going to break something if the pin seems stuck.

Do not push the pin all of the way out or else it will be nearly impossible to put back together.