It's hard to even know if the legs can be corrected. With chicks, the sooner the better to attempt any type of correction/treatment. Right now bones and joints are still a bit flexible and can be manipulated. After a week or two, most leg issues can't be corrected.
Slipped tendon? It's hard to know with chicks.
Hopefully someone else will have a better idea.
https://sites.google.com/a/poultrypedia.com/poultrypedia/poultry-podiatry
https://www.backyardchickens.com/threads/peachick-with-slipped-tendon.1092979/