To loosen the tube on the back of the Prusa XL filament sensor, press the collet ring in toward the fitting, then pull the PTFE tube straight out while holding the ring down. A forum fix for the XL describes the same idea from the sensor side: push the collet on the underside of the filament sensor to release the tube, then pull the tube free.

Safe removal steps

  1. Unload filament and power the printer off first.
  2. Locate the tube fitting on the back of the side filament sensor.
  3. Push the small collar or ring on the connector inward.
  4. While keeping that collar pressed, pull the tube straight out.
  5. If it is stubborn, gently wiggle the tube as you pull, but do not force it at an angle.

If it will not release

The Prusa knowledge base says the XL side filament sensor can be removed and cleaned if normal cleaning does not work, and that this requires partial disassembly of the Nextruder-side setup. If the tube still will not come out, the fitting may be gripping the tube tightly or the sensor may need to be opened for cleaning.

Small caution

Do not yank the tube by itself without pressing the release collar, because that can damage the fitting or the tube end. If the tube end is scarred or flattened, trim a clean square end before reinstalling it.

TL;DR: press the connector collar in, then pull the PTFE tube straight out from the back of the filament sensor.