Right, when you got your Canyon, you will have received all sorts of manuals, bits & pieces, etc. One of the things you got was a long thin plastic tube (nows the time to regret throwing that way).
To replace a cable, you disconnect the mech end and remove the outer and ferrules from the mech end but DO NOT remove anything else.
Next use that thin plastic tube and push it over the inner. Push it on as far as it will go. Then tease out the ferrule and outer from the bar end exit from the frame.
Push the inner AND the plastic tube so it emerges from the frame. You should now have the plastic tube and inner showing BOTH ends of the internally routed cable.
Next carefully pull the inner out of teh plastic tube, leaving just the plastic tube in teh frame with the ends hanging out both ends. Remove rest of inner & outers.
Now, put a new inner in the shifter and add furrules and outer for the ‘bar’ end of the cable rtun. Push the inner through the plastic tube until it emerges out of the other end of the plastic tube.
Pull the plastic tube off and finish cable fitting.
Store the plastic tube safely for next time.
Easy!