Change Domain Name

==== Required information ====
- iRedMail version (check /etc/iredmail-release): 1.8.2
- Linux/BSD distribution name and version:
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): Mysql
- Web server (Apache or Nginx): apache
- Manage mail accounts with iRedAdmin-Pro?
- Related log if you're reporting an issue:
====
Hi all ,
My Company would like to change from  a.com domain to b.com domain on the same server  and keep all user information ( mail data , password ) , the only way I can do is change all record in my database, I need to do it manualy . Could you please show me the easy way to do that ? thank you so much .