You can change MX records 2 ways.
1. From your cPanel
Login into your cPanel. Then go to the "Domains" section. Click on "Zone editor"
Then click on "Manage" option.
Here you can set '0' as the higher priority and in the destination your mail server name.
Login to your billing panel (billing.eicra.com).
Go to your domains list from the option "My Domains"
Click on "Active". You will get the below options on the right-hand side of the window.
Then fill the box using the option "MX (Mail).