On your EXOD.ai Dashboard, you will see on the top bar an Ad Account dropdown.
Press Add New!
You will be redirected into the Ad Account Selection page where you will be able to select the Ad Accounts you want to add to your Account.
Now you can click on the toggle button on the left of the Account's name.
All you have to do now is select which plan you want for that Ad Account.
If you add an Ad Account here with one of the paying plans, if you already have a paying plan connected to one of your ad accounts, your Credit Card will instantly be billed for the new Ad Accounts that you added.