Hi JHS21,
Navigation within a form allows app users to view lists of related records. Each entity relationship has properties to control whether it should be shown.
In general, it will appear as tab after you click it under 'Related' tab, but it can't fixed in the tab.

If you want to view records of the related entity in the tab not navigation, you need create a new tab and add a new sub-grid for the related entity in the tab.

Sub-grid properties:

Save and Publish it.
Test:
