A broken or bent chain ring tooth will cause havoc with pedaling and shifting.
Normally you will bend a tooth on your outer (big) chain ring when you hit this ring against a stump or rock. The bent tooth will then catch on the chain with every revolution while you are in your middle ring. Shifting into your big ring either won’t “take”, or the chain will try and fall off with each pedal stroke.
The best response is brute force and ignorance – bend it back or break it off.
A lever such as a screwdriver or a crescent wrench can be used to bend the tooth back in line. If it cracks during the process, remove it entirely. You may also need to file the area around it smooth. Be careful not to put a kink in the whole chain ring when bending the tooth back.
Tip: removing the ring from the crank arm to carry out this procedure takes longer but may result in a better fix, because this allows you to steady the chain ring while bending the tooth back. It also makes filing easier.