How can I fix this muscle flex deformity? (photo)

Many thanks for the question and pictures.
In the first instance it may have been wiser to have left your implants in the pocket they were in and fat graft over the top to sort out any visible rippling.
The problem you now have is very difficult to sort out if you leave the implants under the muscle as the muscle edge has been released off the chest bone a little too much and now sits higher and is causing the ridge line that you see. Fat grafting can try to disguise this but it is dynamic so will likely be visible on movement of your muscle. The only real option to give you as good a chance as any is to take the implants from under the muscle, repair the muscle back down to your chest wall, place the implants on top of the muscle once again and then fat graft over the top.
You should speak with your PS about this. I note that you are in England so always look for a surgeon that has FRCS (Plast) after their name and check that they are on the GMC specialist register for Plastic Surgery.
I wish you luck.
Marcus

This is relatively difficult to remedy, but fat grafting might smoothen out the ridging.If you do have any concerns of course you must return to your PS for advice and guidance.