If someone's jaw is stucked while yawning what should be the immediate response for this?

Relax: Try to relax (easier said than done). Do not try to close your jaw, but rather try to wiggle your jaw side to side and your jaw might close. Call your dentist.

Try heat first : Try a heat pack but please don't dry and force closed. Try and get into a dentist/tmj specialist asap. Sometimes muscle relaxants are ok, but i don't like to medicate patients. Massage the facial muscles, below the jaw joints and also massage the tissue area behind the upper right and left last molars.

Get it unstuck: Reducing it quickly back into position before muscle spasm kicks in is critical. The jaw needs to be grabbed in the back, pushed down and then brought forward. You actually need to put force on the back teeth and push down to the floor.

See your dentist: If your jaw is stuck or you have lock jaw occasionally a dentist or oral surgeon may need to manipulate your jaw to get it back into the correct position.

Oral surgeon: If this is a chronic problem, you probably already know how to self reduce the jaw dislocation. If you can't, see an oral surgeon during office hours, if after hours, go to ER, ER MDs see this often and know how to reduce. Often required sedation and/or local anesthesia.