video reference here

If you can't access your server anymore then this is not an Odoo problem. So this might not be the best place to look for help in such situations. However, IIRC you need to detach/dissassemble the server's hard disk and to attach it to another computer, then try to access the harddisk's file system. If you have access to the openerp.conf file as described by Raaj, you'll find your master password.

If you want to restore the database backup from the file system of your old server on a new Odoo installation on a new server, you do not need the master password of the old Odoo instance, but the master password of the new one.

Onkar,

Open your configuration file and set new master password

See the example which is working in odoo 10

root@example:~# nano /etc/odoo/odoo.conf

[options]
 
admin_passwd = *****
     
...

Then restart your odoo.

root@example:~# sudo service odoo restart

Hi Onkar please check the below url, hope it will be helpful for you.

https://www.odoo.com/forum/help-1/question/how-to-recover-master-password-if-i-forgot-it-625