Question about AliveCor Ekg device Al-Kardiamobile

I don't know. I had bought it for myself. In the meantime, I use a smartwatch.

...place the dog on its back for the measurement

Preparation (ensure el. conductivity): Rub front paws with conductive gel, if not available hold in slightly salty water.
Measurement: Press left paw on one surface, right paw on the other.
Have fun 💁♂️