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.