I guess with entity you mean object. If your button is on a data container, you can use the object inside of this container as input parameter of your microflow. If it is a nested container, you can also use objects from upper levels. If all needed objects are already available like this, you can just use a change action to overwrite the current values with empty (or with whatever you need). If they are not already available, you need to get them (retrieve). You can also decide if you want to commit them or refresh the page.
I highly recommend doing some of the learning paths in the academy section.