How do I lock door for self cleaning - Ovens

Some ovens have a latch handle between the top of the door and the actual range top that you have to push sideways to lock. May also be a lock button you have to push in while moving the latch handle.
If you don't see the latch handle, The lock system may be the hidden type that should lock automatically when set to clean. Once the oven is set properly for clean, a motor will latch the door by itself. After the oven gets close to clean temperature, the latch gets locked out and the door will not open until the clean cycle is complete and oven cools down to normal room temperature again. This is a safety feature so you can't open the door while the oven is at clean temp (about 850 degrees). Hope this explains enough. If door never auto latches, could be a problem with the latch/lock system and motor.