In the settings section, click Auth. accounts in the column on the right hand side to access the list of accounts of external parties that are used per dashboard, like Twitter, Facebook and LinkedIn. You can revoke access permission from Playr by removing the account from this list.
You cannot delete the account when it is currently being used by one of the apps on one of your pages. In the list you see on what page(s) the account is used. Click on the page name to go to the designer for that page. Remove the app that uses that account, or configure the app to use another account. When the account is not being used anymore in any page, you can delete it.