R.,
Make sure your former husband gives you the necessary paperwork to enroll your child in school. (School, medical records etc.) Do you have a copy of her birth certificate? If you do not, get a copy as you will need this to enroll her in school.
This is an opportunity for you to regain or receive joint custody of your child. It doesn’t matter what he tried to make you look like in court….that is in the past. Don't think of this as chance to fight him again in court, think of it as a chance for you to prove you are a good and responsible mother.
Hopefully he has offered some financial support and/or medical coverage, but if he hasn’t if you are able to support her and provide medical insurance it will be additional evidence that you are responsible.
No doubt your former husband has discovered being a single parent is not an easy task. Happily take your daughter back and wish him well in getting on his feet. Document carefully and quietly any and of all his activities concerning his daughter while she is with you. Phone calls, visits, support etc. After a few months you may have the evidence to prove that you indeed are a fit parent and should have have the custody issue modified in the best interest of your child.
The less you say to him the better except for communicating what needs to communicated about your daughter.
Blessings…..