If you and the other parent have a decision on rights of access from the State Administration or an agreement enforceable by the bailiff’s court, you should contact the bailiff’s court. The bailiff’s court can help you get the child back if the other parent does not observe the agreement/decision.
If you have made an oral agreement, or you have a written agreement that is unenforceable, the bailiff’s court cannot help in making the other parent return the child. Instead, you should contact the State Administration and apply to have custody transferred to you or ask for a decision on rights of access that is enforceable.
You can find more information under the subject Not returned from access.
You can find information about the determination or modification of rights of access at The State Administration's website. Read more here
You can find the nearest bailiff’s court at: domstol.dk.