You're almost there. The only thing you have to do is using a different object like an "Update object" instead of using the same "Issue object". In this "Update object" you can use the user input and perform the actions with this user input.
Then you have to create an association from your "Update object" to the issue object, so that it can refer to a number of issues. Then, create a form with a data view on "Update object", which contains the fields that you want the user to enter, as well as "OK" and "Cancel" action triggers (customized buttons).
Trigger a microflow from your data grid, create a "Update object" object and fill the reference to the Issue object with the selection that is passed to the microflow. Then open the user input form with the 'Update object" object as parameter.
In the microflow you can use the "OK" button and use the reference from the passed "Update object" to the Issue object to retrieve the selected Issues. Then update all fields. Also delete the "Update object" like you described in your question to clear up the database. Finally, close the form.
In the "Cancel" microflow (which you trigger from a customized Cancel button) you only need to delete the "Update object" and close the form.
It's almost the same issue as described here.