First, navigate to the campaign where you'd like to connect the Pinterest integration, then click "Integrations" from the menu on the left side of the screen.
Click on Pinterest in the list of available integrations.
Then click Connect New Account.
Next, you will be asked to log in using your Pinterest credentials.
Note that if you're already logged into Pinterest in your browser, Pinterest will automatically connect the account you're using. To avoid this, go to pinterest.com and log out, or choose "Not your account? Log out." on the authorization screen (shown below).
You'll then be prompted to connect your account to Pinterest. Click "Give access" to confirm the connection.
Once connected, your Pinterest data will appear under the Social > Pinterest left-side menu option.