To edit your MX records in WCP you will first need to login at

Once you have your domain loaded click on DNS Editor

You should have a current default MX record listed.

Click on the edit icon next to that record and change the Data and the Priority to the correct settings.

Leave the Name as just the @ symbol (This is the most common issue if your new MX records are not working)

If you need to add another MX record click on Add DNS Record, Enter @ for the name, change the type to MX and enter the Data and change the Priority level.

The priority level sets an order for the emails to try to be delivered. The lowest numbers are attempted first. The most common settings for this is usually 5, 10, 20, 30, etc...