Once assembled, you can install the hotend like the stock Bambu lab one.
To change the nozzle heat the hotend up to 240C for 5 minutes, then unscrew the old nozzle, install the new one and gently tighten the new nozzle.
When unscrewing the nozzle quickly turn the wrench or socket - while a wrench is included we do recommend using a socket (4.0mm Size) if you are new to changing nozzles.