If the door has no manufacturer label (nominal door) can you still carry out repairs to door & if so how would you know what seals & locks to put on if you have no information about the door.

Consult a competent fire door inspector.

They would examine the fire door assembly and then be able to advise about what can be done to improve its likely fire/smoke resistance performance. But remember, even after the works have been done a nominal door is still a nominal door.