You should drain the engine coolant, disconnect the inlet
Heater Hose from the heater core inlet tube, install the J 43181 to the quick connect on the outlet heater core hose, close the tool around the inlet heater core hose, firmly pull the tool into the quick connect end of the heater hose, grasp the heater hose, pull the heater hose forward to disengage the hose from the heater core, position the inlet heater hose clamp at the engine block using J 38185 and remove the heater inlet hose from the inlet hose fitting at the engine block and the heater inlet hose.