Hi Martyn,
What you can do is first create a button on your data grid with a microflow behind that gets the details. Your user can then select one of your customers and click the button after selecting by which your selected customer is passed to this microflow.
Secondly, if you like you can configure this specific button to ‘Is default button’ on true so that when your user double clicks on a customer your microflow that belongs to the previous button is triggered automatically as well.
Hope this helps!
Cheers,
Mark