A 90 degree adapter to go from a rectangular cable channel (https://www.amazon.com/dp/B08MT99QLG) to a quarter circle one (https://www.homedepot.com/p/Commercial-Electric-5-ft-1-4-Round-Baseboard-Cord-Channel-White-A60-5W/304502804).

This corner doesn't “snap” onto the channels like their included corners do, so you may need to tape them together if you plan to use it in a dynamic environment.