To fix this you need to find the barrel part of your lock.
How to open a door with a broken lock barrel.
To rule out any problems with the cylinder try inserting your key and turn to unlock.
If the locking mechanism is a latchbolt the kind of bolt that is spring loaded and has one angled edge and the angled edge is facing away from you you can hook it with a wire hanger.
As previously noted this skill takes a lot of practice to master so have plenty of cheap practice locks on hand if you hope to get good at it.
And this will need replacing.
Grab the broken knob and pull it from the door.
Depending on the manufacturer the spindle may pull from the latch or slide off the spindle.
So all you would need to do is find the screw that holds the barrel of the lock in place and tighten it.
This is found where your indent for your key is.
The gearbox is an essential part of the locking mechanism found in the door.
If it turns freely and unlocks then the problem may lie in the multipoint lock.
I got a hammer and beat on the door knob until it broke it off.
This will tighten the loose door handle and if done correctly your upvc door should be locking correctly and working again with no issues.
Then the door opened.
Use the leg of the pick to find and push each pin up and out of the tumbler.
Insert the pick above the wrench.
Then i got a big screwdriver and used the hammer like a punch to knock out the remaining parts of the lock and latch.