Hi,
I'm Rodrigo and I'll help you.
The format process is not reversible.
Use CMD to convert to GPT to be able to reinstall Windows, but to recover your files you will have to use a file recovery tool.
To convert the disk to GPT, press Shift + F10 to open the command prompt and follow the instructions on the link below:
https://learn.microsoft.com/en-us/windows-serve...
Here is a free tool you can use to try to recover your files after installing Windows
https://apps.microsoft.com/detail/9n26s50ln705
How to use the tool: