I do this most days easiest way to do it is to insert follower bar thats the technical term for the spindle into the door handle and through the latch in the door ensure door handle is.
Thru spindle too short on door handle.
The one that screws into the larger flat.
Hold the knob in one hand and insert the other end of the spindle into the square port inside the door lock.
If that does not work try and use a thin scraper or similar to disengage the latch from the gap between door and frame.
One knob is fixed permanently to the spindle by means of a grub screw through the neck of the knob.
Remove the set screw securing the doorknob to the spindle then unscrew the door knob off of the spindle.
It s nice being able to get through your door without too much trouble.
Try and use a big flat screw driver to open the door where the spindle use to go.
Once door is open remove old latch and replace.
Unscrew one handle and remove the spindle.
It seems the original had broken so it actually was too short to fit where it belonged.
Remove the rosette off of the spindle.
Remove the knob and rosette from the other side of.
The other end of the spindle and opposite knob is threaded so that this knob can screw on to the spindle and subsequently adjust for door thickness.