How to connect bluetooth headphones to phone without know the model I have old bluetooth headphones that I try to connect to my device. I don't know the model only the brand name.

The question is how to pair it?
You can look for insturction for the brand name. Usually the insturction is the same for all models.

Example for my original question about plantronics:

pairing-instructions-for-all-plantronics-bluetooth-models