Type in the console» bind g bsmod_killmove «and press Enter to confirm. Or just copy and paste it.
You can change the key by replacing the letter "g" with your preferred one.

The "bind" command is from Gmod itself to tell another command to run after pressing that key: bind (a key of your choice) to the "bsmod_killmove" command.

Be sure to use spaces between the commands and a underscore in "bsmod_killmove".