Being on iPhone you’ll likely find this a lot more difficult as Android offers multiple solutions (using ASUSWRT, Tasker + Sharptools, etc).
Your best presence options will likely be:
Life 360: https://support.smartthings.com/hc/en-us/articles/202334244
ST Presence fob: https://shop.smartthings.com/#!/products/samsung-smartthings-arrival-sensor
Automatic for your car: [RELEASE] Automatic Connected Car- Integration with SmartThings