For Mythic Plus progress, you do not need to mark a character as Main. This is done automatically based off which character has the highest score on your Raider.IO account. However, you do need to mark a main to designate a main for your raid progress. To set a main:
1- Log in to Raider.IO and navigate to your Settings.
2- Select the desired character to be your Main from the left bar.
3- Check 'Mark as Main Character.' then click 'Save' (By default, this is all you need to do. However, if you want to confirm it will show on all your alts, continue reading.)
4- Select the alt that you want to have to display a link to the Main character.
5- Check 'Include Link to Main Character on site and RaiderIO Addon.' then click 'Save'
Note: All characters must meet our minimum requirements in order to show up in the addon, even if the main character far surpasses them.