The A1 changes the complete hotend rather than asking the owner to wrench a hot nozzle from a heater block. Buy a compatible A1 hotend in the required diameter and material.
Unload filament, park the toolhead and let it cool fully. Power off the printer. Remove the toolhead cover, disconnect the hotend retaining parts and release the hotend only in the order shown by Bambu’s A1 hotend guide. Do not pull on heater or sensor wires.
Seat the replacement squarely, lock it, reconnect the parts and reinstall the cover. On startup, set the installed nozzle diameter in the printer and Bambu Studio. A physical 0.6 mm nozzle with a 0.4 mm profile will produce incorrect extrusion.
Run calibration and print a small first-layer test. Stop if temperature is unstable, plastic leaks above the hotend or the cover does not sit normally. Those are installation faults, not flow-calibration problems.
Choosing the right diameter matters beyond just this swap — the nozzle size guide explains what changes in flow and detail once you move past 0.4 mm. Regular checks from the A1 maintenance schedule are what usually catch a worn hotend before it fails mid-print. If the printer raised an alert rather than showing a gradual decline, the HMS error index is the faster starting point.