Can't reset Craftsman garage door opener
The most common cause of the door reopening is that one of the door limit switches is dirty or misadjusted. There are different switches to detect door travel and to sense the torque applied by the motor. The example below shows the switch that closes just before that door reaches the bottom of travel.



The two limit switches are at the end of the support rail. Try cleaning switch contacts, which get greasy from the rail lubricant.  This is easy to do since contacts are exposed on many Craftsman door openers (not a hazard, since only 24 VAC at low current is used). Use automobile brake spray cleaner or other nonflammable, non-toxic (or only mildly toxic), solvent. The contacts are just below the end of the wire. If the door is open, you can clean between the leaves of the contacts with a cotton applicator -- being sure to remove any lint.

If that doesn't resolve the issue, loosen the switch from the rail and adjust forward or backward until the door closes properly and stays shut.

The purpose of the bottom switch is to sense the last few cm of door travel. The torque-sensing switch in the motor housing reverses door-travel direction if an obstacle is encountered, such as a child's foot on the door sill. However, the door must close with enough force to make a tight seal, preventing bugs and drafts from entering, so the bottom limit switch disables motor reversal as the door touches the sill. If that switch fails to close, the door reacts as if an obstacle caused it to reverse... sometimes, after a delay of a few seconds.