In the top right drop-down menu, select SUBSCRIPTION PLAN.

On the subscription management page, click on "Link Google Ads account: Sign in with Google".
​

You will be taken to Google's Authorization pages. Follow the steps until you're brought back into Tenscores and your new account will be listed in the left box on the subscription page.

To activate a new account, select it then click the "Update subscription" button in the lower right.