How can ypu help someone get their mental physical and social health back to normal if they are underweight or overweight?

Encourage them.

Explanation:

This is a really good question, and I'm not 100%.

I think that to help with their mental health you could for sure encourage them. Build them up. Help them acquire their self confidence. Just be there for them you know? Physical and Social? You could invite them to go with you to go and do certain things. Go attend a party together or something..(not in these times but you know what I mean).

Also, it isn't always a bad thing to go ahead and encourage them to get help with whatever they might be struggling with. Doesn't matter who it is, anyone can get help if they need it.

Hope this helps! Good Luck.