I am unable to do the 9th exercise of the "Unlock Your Hip Flexors" program due to C1/C2 fusion any planking modification?

Considering your condition please note the Unlock Your Hip Flexors program offers modified routines that make the exercises doable. We call it "exercise swaps" and you will be given access to these modifications once you purchase the program. Exercises that may be too challenging such as plank on the floor can be done in alternate positions like standing. Other alternate positions offered on the different exercises are sitting, kneeling, and lying down.

For more support for the Unlock Your Hip Flexors program, please submit a ticket here.