Use the P1-series procedure for the hotend version fitted to your printer. Unload filament, let the toolhead cool and power off before removing its cover.
Disconnect the fan, heater and thermistor plugs by their housings. Never pull a plug by its wires. Release the hotend fasteners, support the assembly and transfer only the parts named by Bambu.
Seat the replacement fully and route every wire as shown so the cover cannot pinch it. Reconnect the fan and sensors before closing the toolhead.
Set the correct nozzle diameter in both printer and Bambu Studio, then run machine checks and a short extrusion test. Stop for an unstable temperature, fan error or plastic leaking above the heater. Hotend wiring and heater faults are not safe places to improvise.
Picking the right diameter for this swap is covered in nozzle sizing beyond 0.4 mm, and if the choice is also between brass and steel, that trade-off is laid out in brass vs hardened steel nozzles. Once the new nozzle is running cleanly, fold it back into the regular P1S maintenance schedule.