Maybe someone will find it useful.
If your MyChron gets stuck and you cant modify settings, upgrade FW, erase sessions, tracks or anything else. It powers up without menu icons, only text description on the screen. You can try this to completely erase its ROM - erase current FW and all data.
This is the instruction I got from AIM support for my 5S 2T:
1 - update your software Race Studio 3 at latest version or upper (currently 3.72.08) and after download Mychron5s firmware version (2.42.16)
2 - Turn on Mychron in booter mode, holding pressed the two left buttons while pressing the ON button. The red LED will blink and the display will stay blank
3 - Connect MyChron5s to RS3 through WiFi
4 - Go to the Download panel
5 - Press Ctrl+Shift on PC keyboard and contemporary click on the cogged wheel on the right of the window A menu - will be prompted, select “Format and Erase all devices memory”
Mychron5s will restart with small fonts, all data and settings inside shall be cleared. (My device didnt restart on its own. I had to remove the battery after 5-10 minutes)
6 - Switch off Mychron (of course, it switched off when I removed the bat.)
----wait few minutes before replacing it.
7 - Turn on in booter mode, holding pressed the two left buttons while pressing the ON button. The red LED will blink and the display will stay blank.
8 - Connect via WiFi at RS3
9 - Execute the firmware update to version 2.42.16 (or latest suitable for your device)