This is a gcode I scripted for the Ender 3 Pro specifically. It should work on most printers.

It is designed to auto home, clear the bed, preheat the bed to 70 degrees, and then shut off the heat. The whole process takes about 90 seconds.

Set your smart device centered on the printer bed before running the gCode. Then remove the screen and continue with your electronics repair once the code has run it's course.

Special thanks to: u/Coquinha_gelada_hm

[OG version] shuts down immediately after reaching 70 degrees because it has no wait feature (I will set my phone on the printer and then start the process so the device is warmed up slowly. After 90 seconds, when the code is done running, the device is typically ready to pull off and repair.)

V2 has a WAIT feature in the gcode. If you open this in a text editor you can change the amount of time the device waits before shutting down the bed. V2 waits 10 seconds and then shuts down.