I suspected the answer was going to be “nothing” and it’s a concept I find quite strange.
So Blynk has nothing to control.
Ignore my rambling it’s sleep deprivation and a different mindset I have about iOT.
That said have you considered hooking up a $3 MCU to Blynk and writing a few lines of C++?
Until such time as Blynk adds the map widget to the API then I think the line above is the only solution for you. It doesn’t have to be C++ and you can use the Pi that’s hooked up to the GPS device if you wanted and have the correct coding skillset.