The Raspberry is a minicomputer that has its operating system installed in a microSD, like that of smartphones
Retropie is the software that allows emulators to work on the Raspberry system
If you intend to perform changes and you do not know if they can be successful, perhaps it is better to create a BACKUP microSD, so if something goes wrong you will have the possibility to restore the system correctly functioning.
Or the backup can be useful in case of failure of microSD, more frequent than you think.
Below I explain the step-by-step procedure, to be carried out with a Windows PC

Software required (for Windows) :
• Win32DiskImager - to create a backup .IMG file from a microSD

https://sourceforge.net/projects/win32diskimager/

• BalenaEtcher - to restore the .IMG file to a new microSD

https://www.balena.io/etcher/

ATTENTION - Before proceeding, make sure you have enough space on the PC: If you need to backup a 256GB microSD, your PC will need 256GB of free space
If you already have a previously saved .IMG file or if you have found one on the web and you want to try it, go to point 4)

BACKUP PROCEDURE
1) Connect the "source" microSD to the PC through the appropriate slot (if available in the PC ) or via a microSD / SD or microSD / USB adapter.
2) Open Win32DiskImager to generate the .IMG file to be copied to the new microSD
- Start Win32DiskImager and in the "Image File" text field choose the path to save the file, and the name of the file

for example C: /Utenti/Utente/Desktop/imgRaspberry.img
- Using the "Device" menu choose the letter corresponding to your microSD.
- Start the procedure using the "Read" button and wait for the end. (Attention the procedure could take a few hours depending on the size of the microSD).
3) Extract the source microSD from the PC, now in the path you have previously selected you will find an .IMG file that will be the backup copy of your card.

RESET PROCEDURE
Now that you have the .IMG file saved, you can load it into a new microSD
4) Insert the new microSD in the PC slot and start BalenaEtcher
- Select the .img file obtained earlier via the "Flash from file" menu
- Select the target microSD via the "Select target" menu
- Press Flash and wait for the end of the procedure
5) Insert the cloned microSD into the Raspberry slot and start.