DIY question here. My front door knob has come off screws and all. A huge chunk of filling has come out as well. Impossible to screw it back on.

Its become impossible to close the door from the outside as there is some resistance when closing. I have been unable to locate then culprit but either its some of the door that has been damaged inwards (at which point sanding is the most viable option) Or its coming from the badly fitted door knobs. So what should I do?

Should I try repair it myself or will a locksmith sort this out? Or is there another more adapt service available as its not technically 'lock' related?