You could do something like this:
- Create a table with a single row, and use this as the source of your screen
- Add a RowID column, and a User Specific column for each of your form inputs
- The first one will be for the MembershipID. Create a relation column that matches this with your Subscribers table. As long as this relation remains empty, that means they haven’t entered a valid ID.
- Add your input components to the screen. For all of the components other than the Membership ID one, you can use the state of the relation column as a visibility condition. ie. only visible when the relation is not empty.
- Add a button to the screen. Configure an action on the button that adds a row to the appropriate table, using the values in the user specific columns as inputs.