How to get location of user/device that started the flow

I want to make a flow, such that you can turn on the heating at home, when you are underway to home. It should check the ETA to home, and based on that, directly start the heating, or delay the hing start, based on the ETA, e.g. it should start when ETA is e.g. 20 min from home. To get the eta I want to use Verwachte Aankomsttijd Google Maps, but I don’t know how to get the location of the device/user that activated this flow.

Rob van Gestel mentions in the description that you need an app like ‘geofency’.

Yes, but there it says: When you leave work, an app like Geofency on your phone can trigger a webhook to Homey.

But I want that I start the flow manually, and the flow gets the location of the device that triggerd that flow. And that is unclear…