Is the service object connected to the location?
You can then pass the location object and retrieve the service object in the microflow that is triggered when clicking on the button.
As far as I know it is possible to pass 2 parameters to a microflow from a data view. Regarding to Mendix: "if the widget calling a microflow is contained inside a nested data view, then the object of the enclosing data view is also available." Can be found on: https://docs.mendix.com/refguide/starting-microflows#3-microflow-arguments
Hope that helps.
The dataview that has the microflow button and is listening to the unit grid, needs to be moved out of the datagrid of Location. If you move it down so that its in the dataview of Service, you can pass the "Service" and "Unit" as parameters in your microflow. If you need location in that microflow, I'm assuming it has a relation to unit, so you can retrieve over association to get location.