I will use a address and postal address example. If the user fills in his address on the form and you have a tick box that says the postal address is the same as address you what to fill in the postal address values automatically when the user checks the tick box.
To do this place an event microflow on the on change event of the tick box and run the microflow. In this microflow fill in the postal address values using the address values. Place a refresh on the postal address object before ending the microflow.