Adding additional Target Objects for Group Assignment

1. Navigate to Setup and select Object Manager > Assignment Group.

Note: If using Salesforce Lightning, navigate to Setup, then search for and select Object Manager. Locate and select the Assignment Group object label. Click the Assignment Group object.

2. In the Custom Fields & Relationships section, select the Target Object field.
3. Update the Picklist Value Set with the API name of the new Target Object.
4. Save your changes.
5. Create your Group Assignment Custom Settings.