I need some tips on caring for curly hair

My boyfriend had really nice curly hair but his last girlfriend hated it so he straightened it everyday and now his curls are all messed up. Lately he’s been asking me for help since I’m very good with hair care but I have stick straight, thick asf hair and have no clue how to care for curly hair.

Can anyone give me some tips on how to care for curly hair bc I’m seriously at a loss