It's automatic.
Depending on location, it may take a couple of minutes for the Spark to establish a Home Point.
There should be an audio prompt and message stating the " The Hompe Point has been updated, please check it on the map."
Watch the flight bar at the top and it should go through 3 steps as the Spark collects data.
Attitude mode, GPS no home point, GPS with home point.
The rear lights of the Spark will flash green when the home point is established as well.
If you miss the audio prompt, and the lights are green, check the map box for an "H" drop pin.
Sometimes I may miss the audio prompt and I check the map for "H". Once the motors start, the audio prompt usually repeats and good to go