How can I change these plastic backing strips in this chair?
I have another chair exactly like this one, but the white plastic strips are broken.
You've got to pull the band toward you when you're at the edge of the chair and get some slack where the band goes around the frame. Then use a screwdriver to gently pry the band out of the slot on the frame. If it's an old band there's a chance it will break when you try to pry it out. If you're successful then do the other side. Installing them is just the reverse. Good luck/
I had to do this for someone once. Jack is correct. I don't know where they got the bands, but I found that if you soak them in boiling water for a few minutes, they become much more plyable and then tighten up as they cool down.