Originally posted from the original by philltran - https://www.printables.com/model/339966 - additional steps in italics.

Each spool requires one core adapter.

• Remove the RFID tag from the original Bambu Lab cardboard core that you wish to reuse - make sure to remember which side of the tags face outwards
  
• Remove one cardboard sides off of the original spool.
• Place the spool on a sturdy surface with the open side facing up.
• Insert the adapter into the center of the spool. Make the edge of the adapter flush with the edge of the cardboard core. The adapter has a slot to line up with the notch on the Bambu reusable spools. Make sure slotted side of the adapter is facing out
  
• Add the RFID tag removed earlier through the thin slot - it may be quite tight if some glue remains from the original tag. Fold the tags up to lie flush with the new filament
  
• Separate the Bambu reusable spool into two parts.
• Insert the Bambu spool section with notch onto the spool core so that the notch lines up with the slot on the adapter.
• Holding the spool together firmly, flip over the spool so that the remaining cardboard side faces up.
• Remove the remaining cardboard sides off of the spool.
• Insert the remaining Bambu spool section onto the spool core.
• Rotate the Bambu reusable spool sections until the two sections “click” together.

Originally remixed from Dustin Tebo's Protopasta Bambu Lab spool adapter (https://www.printables.com/model/320144-bambu-lab-spool-adapter-for-protopasta-spools/remixes)

Direct remix of philltran's Bambu Lab Spool Adapter for Polymaker PolyTerra Cardboard Spools