Triple antibiotic ointment like Neosporin if you have that available in England.
Is vet care an option at all? If so, that would be best.
The older a chick is, the harder it is to correct or fix leg issues. If the joint is still infected, then that needs to be addressed - a vet can...
The joint looks like it may be infected and it's probably slipped as well.
Clean the joint/scab with an antiseptic and apply an antibiotic ointment.
If the tendon is slipped, you can try correcting that. I see you've been given info on that in previous posts.
A 6 day old chick needs to be...