2 month old male muscovys legs keep slipping

[Miss Lydia]

Okay look at the other one who hasn't a leg issue see where his/her legs are sitting under their body. That is how you want to fasten the hobbles so the legs are sitting in normal position underneath the body. Be sure to give this little one swim time too so he can keep his leg muscles strengthened. It will be a pain to take the hobbles off and on so once you get the hobbles fixed so the legs are sitting normally maybe wait a few days before taking them off for swimming.
@CoriM has more experience with hobbles.

 

[CoriM]

I would also pull the legs together so they appear normal - just like your other ducks. It won't hurt him if you just move them gently and he'll get the hang of moving around with the hobbles on. It's really the only chance he has to start developing normally. How's it going with the vitamin B complex? Make sure he's getting plenty of that.