Explanation:
Graphical user interface, text, application Description automatically generated

Step 1: Add a Subgrid component to a form
You add a subgrid component the same way as you add any other component.
Step 2: Select Show related records and then select the related entity and default view for the subgrid Configure a subgrid component.
Properties available to configure when using a subgrid component on a form using the form designer include:
* Show related rows
When selected, the subgrid displays only rows related to the current row that is displayed on the form.
Step 3: Select the Allow users to change view option
Configure a subgrid component.
Properties available to configure when using a subgrid component on a form using the form designer include:
* Allow users to change view
When selected, app users can change from the Default view to another view of the table selected in the Table property.
Step 4: Save and publish the form
Reference:
https://docs.microsoft.com/en-us/powerapps/maker/model-driven-apps/form-designer-add-configure-subgrid