The sealed aluminum thermostatic probe is simply inserted into through the top of evaporator box and into the fins between the tubes in the evaporator. "Usually" the probe had a brass sleeve with it, the probe inserted into the brass sleeve and the sleeve with probe goes into the fins of the evaporator.
You can gently pull the probe or probe with sleeve directly out, BUT be careful not to bend or break the aluminum probe because it is a thin wall tube filled with refrigerant gas (the gas expands and contracts) and it is crimped sealed on the end. If you break it you will need to a new one.
Discussed here