Eventbrite login with "social buttons" (Google, Facebook..) is not supported on external apps. Please, choose login with email and password. If you don't have a password associated with the email of your Eventbrite account, then choose Password Recovey to create it.
Alternatively, disconnect the account following the steps:
1) Enter your Eventbrite account with browser (Chrome, Firefox or Safari)
2) Access the "Account Settings" section
3) Access the "Account Connected" section
4) Disconnect the account
If the problem is not solved, please contact the customer service from the dedicated section.