When the annual instrument calibration has been performed on your M937xA module, you will notice that there is no room on the front panel for the traditional calibration 'sticker'. Instead, the calibration date and (next) calibration due date are appended to the M937xA Help About page.
The Calibration date is edited when you send your M937xA module to Keysight for Instrument Calibration.
You can edit these Help About fields, as well as set the calibration interval, using the SYST:SERV:VER SCPI commands.