Step 1 : Click on Integrations tab in left menu, and then click on Add Integration button to add new integration.

Step 2 : Select Twitter from the select list and click on Save Integration

Step 3 : Click on Authorize App button on Tumblr Auth Permissions Page [if you are not logged in into Tumblr you will be asked to login into Tumblr to view auth screen]

Step 4: Once you Authorize ContentLAB to access your Tumblr account, you will be redirected to Accounts listing page where you will be able to view the connected Tumblr account, this way you can add multiple Tumblr accounts into your contentLAB account.