Olá @Seph123.
Infelizmente essa funcionalidade não está diretamente disponível para nós.
Eu recomendo que você encaminhe um e-mail para qtaccount@qt.io.

@matobodo Thanks! The links helped.
Get process id from GetCurrentProcessID() & ProcessIdToSessionId() gives you session id by inputting process id.
#include<windows.h> to access these methods.

I forgot to mark it solved before, sorry for that. I marked it now ;)

Anyway, yes. My new username should've been T3STY_1 (since it said T3STY was already taken i had to pick another one). But right after I posted I noticed my username became T3STY (the username I had in my <old> account) and the old account was merged into the new account. That's just great!