Grandstrem Ip phones and Elastix server

[SCA IT services]

Hello everyone, does anyone here have the IP phones by Grandstream, model GPX 1620? They were down, then I uploaded all the MAC Addresses and IP on its software and It worked, but I cannot access the Elastix server because I coudnt contact the previous person who was working here before I arrived. How can I recover the access credential for the PBX service and the server? Is there a way? has someone gone through this scenario of not having the passwords for accessing the server? Thanks in advance.