Start by trying to push the lock button.
Thumb press door handle sticking.
The most common cause of sticking door handles is some kind of malfunction within the tubular latch itself.
Remove the cap on the graphite powder.
Once you let go of the knob grab the end of the latch bolt with your fingers and pull.
Squirt the bolt with graphite powder.
The issue a door latch stuck due to a jamming latch will have no real variation between how the latch moves when it is pressed in or when the handle is turned both when the door is open and when it is shut.
Turn the knob to open the door and release the knob slowly.
Turn the handle of the doorknob to expose the bolt.
Release the button quickly try sliding your finger off the button so the pressure is maintained up until the precise moment of release with no backing off.
Push and hold the button in.
To test this firstly open the door and check that there are no obvious obstructions on the tubular latch plate such as loose screws or signs of internal parts of the latch or lock poking through.
If the latch bolt doesn t move and is fully extended the issue is with the strike plate.
If the latch bolt moves it is sticking in the door knob and requires some disassembly to fix.