DELL Latitude 5310 (8FC8) with valid warrenty / service and LOCKED BIOS PASSWORD

Hello there

i bought a used DELL Latitude 5310 (8FC8). It have a valid warrenty and service.
Unfortunelly i dont know the BIOS Password. And i am not able to contact the original owner any more
After a call with technican support, they provided me a master code witch is also not working

Any one can help me? How can i unlock the BIOS?! I cant even update it !!

Thank u very much in advance