How do I replace the toner cartridge on the HP LaserJet Pro MFP M426/M427?
Press the front-door-release button, open the front door, and remove the used toner cartridge. Remove the new cartridge from its packaging, hold both ends, and rock it 5-6 times before aligning it with the tracks inside the printer and inserting it until firmly seated. Then close the front door. (Page 31-34)
From the official HP Laserjet Pro Mfp M426 M427 F manual, page 31
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