What is the procedure for an air traffic controller after a major crash or incident occurs on their watch?
Most units today will have some sort of CISM procedure.

Critical Incident Stress Management (CISM) is the structured assistance for a normal reaction to an abnormal event.
CISM methods are secondary preventive measures which consist of discussions about the incidents in the form of structured individual and group discussions and help the persons affected regain their ability to apply coping strategies. Most of the time these discussions are performed by colleagues who have qualified in CISM programmes (the so-called CISM peer diffusers or CISM peers) or by Mental Health Professionals (MHPs) who are qualified CISM experts. None of the CISM techniques can, or should be, regarded as psycho-therapeutic measures.

Read more at skybrary: https://www.skybrary.aero/index.php/Critical_Incident_Stress_Management_in_ATM