Neil,
Microflows can't request (and wait for) user input.
To do this, you could:
Hope that helps,
Mike
*Edit*
Not a dumb question at all - I should have covered this in my original answer.
- Create an association between the helper entity and the datagrid entity
- Add a parameter to the microflow that creates the helper entity. This new parameter should be a list of the datagrid entity. In this microflow, set the new association you created above to the passed in list of objects
- In your datagrid properties, make sure you have multi-select of some sort configured(screen shot below), unless you want all datagrid objects to be passed into the microflow
- now you've got the objects you want attached to your helper entity, you can retrieve them in your second microflow via the association
- NOTE: this approach means your Action button needs to be in the datagrid control bar, like this: