Hi @Clarion 11,
To apply for a residence permit according to paragraph 28 you need to make an application in writing with your local immigration office (Ausländerbehörde). You will need to send them a copy of your passport and the child’s birth certificate. If you are the father and your name is not on the birth certificate, then you will have to submit a recognition of paternity (Vaterschaftsanerkennung). If there is an agreement on shared custody (gemeinsames Sorgerecht), this should also be submitted. If you need any more help with this, let us know.
Best,
Éanna