Go to Add-ons > Get add-ons to install MultiBaas for Google Sheets.
Type multibaas as the search keyword.
Click on the MultiBaas item and then click Install. You will see a pop up to approve permission. Select your account and Allow for permission scopes. You can revoke this approval here at any time.
To set the deployment ID, navigate to your MultiBaas deployment. Copy the URL from your browser's URL bar.