[OnePlus 9 Pro] amaroney55:
Ok this procedure is the way I did it and I have tested it over and over still working to unbrick and even brick your phone. So please use at your own caution I am no way gonna be held responsible for anyone bricked phone. And your data will be formatted erase poof gone if you don't back it up. And I encourage y'all to read Craznazn post.

https://xdaforums.com/t/how-to-unlock-the-t-mobile-bootloader.4256319/

Actually he has several post I used like this one too steps with oneplus 8t works on 9 pro too.

https://xdaforums.com/t/guide-convert-tmo-to-global-eu-or-other-variant.4188491/

Big thanks to him for finding out bout the most important part the modem....

Here we go... I am assuming y'all know adb and fastboot so leaving that out. But make sure you have latest oneplus drivers and adb cause fastbootd has to be used when flashing.

First read Craznazn post on unlocking bootloader. And he has a t-mobile magisk patched link you can use to flash read his post. After your backed up unlocked and rooted. Get this app from play store.

Partitions Backup & Restore - Apps on Google Play

Backup your important partitions to avoid any data or IMEI corruption

play.google.com

I went ahead and checked everyone of the blocks.View attachment 5284881View attachment 5284881

looks like this. Now this is gonna take a a min like 45-1 hour this is your phones active firmware. Mine ended up being 26gb. . While that's going go ahead and and get eu or global your gonna use from xda post or oneplus site full version only. I did global first could not update so I went ahead and did the eu ba 11.2.3.3 (updated one) everything is same works great.

After download use the payload extractor I hope y'all know how and what that is if not please stop and research. Label that folder after it's done global(eu) so I won't get confused. (Go ahead and patch the boot image if u want root);

Now on your phone find the zip file partition backup made for ya. Transfer it to pc. Extract it. Your gonna see some .img and .gz. it's gonna look like

( On the .img file I went ahead and erased the 2021-04-15 part)

View attachment 5284881View attachment 5284893

Then I but both roms side by side and this is very important what I did was took the boot.img and renamed it to orginaleu/globalboot.img from the global/eu folder and placed renamed the magisk patched to boot.imgand place in the global folder.

IMPORTANT IF YOU WANT DATA TO WORK AT ALL. TAKE YOUR MODEM AND MODEMST1 AND MODEMST2 FILE OUT OF YOUR TMOBILE FIRMWARE FOLDER COPY THEM TO THE GLOBAL/EU FOLDER IF NOT YOUR NOT GONNA HAVE NO DATA NO SERVICE AT ALL. AND TAKE THE CARRIER.IMG FILE FROM TMOBILE FOLDER AND COPY IT OVER TOO.

I made this flashall.bat it worked just fine. I might have left out a few partitions but it is all good. Now on pc open a blank text document and copy and paste the change2 flashall.bat.txt and save as flashall.bat. put one in each folder and there conversation folder in one and the recovery folder in the t-mobile firmware folder. To flash just adb reboot bootloader then fastboot reboot fastboot. Make sure your in fastbootd. Screen will look like the recovery screen but it will say fastbootd. Once there click on the flashall.bat and let it do it thing. It may take like 5 mins to boot. Now if it stuck on the oneplus boot animation. Go back to. Fastboot and -- set-active =a or b. And if your rom acts little jumpy or crazy go back and check the boot.img u flashed might hot them mixed up.

My first guide maybe this will help you til the msmtool is ready. I know it get frustrating sometimes that's why I tried to describe much as I can