Add a table as a lookup option in your app
With model-driven apps, for a table to be available in a lookup it must be added to the app. For example, contact records have the ability to be assigned to a user or a team. Both of these tables have a relationship with the contacts table.
However, if the User table is included in the app but the Team table is not, only user rows will appear in a lookup.
This can be resolved by adding the Team table to the app using the App Designer.
Add a related table to an app to enable the lookup
Go to Power Apps, and then select Solutions. If the item isn’t in the side panel pane, select …More and then select the item you want.
Open the solution you want, and then select the model-driven app. This opens the app in the app designer.
Select the Components tab, select Entities (tables), and then select Team.
Select Save, and then select Publish to make the change available to app users within the organization.