Requirements : Rooted Samsung Galaxy Note9 Exynos (SM-N960F/FD/N)
WITHOUT ROOT ACCESS THIS APP WON'T WORK.
It is small utility to backup/Restore EFS for Smamsung galaxy NOTE 9

Features :
This tool simply Backup/Restore efs.img partitions.

Installation
-You must have device ROOTED.
-Enable USB debugging
-To make backup - select EFS Backup Restore SMG N8/S8

From next screen you have to press backup option icon, Backup files will be stored to MyEFS folder as well MyEFSbackup/myEFS_mm_dd-yyyy-hr-mm_Device IMEI folder on device storage. This will make backup of required partition Also you will found build.prop file in backup folder, which is just to get information about your ROM while backup was created. Also last backup will be saved in MyEFS folder on device storage.
In case your device varient variant doesn't supported then will get notification about this. from same screen you will have option to mail to developer for issue.

-Auto backup - This is experimental feature. You can enable/Disable it from Backup/Restore menu page. Selecting this option will make auto backup when there is a new ROM version found. ROM version info will be collected from build Display ID. Any manual changes to this also backup will be created

-To restore, This will use last backup stored in Device storage/MyEFS folder. Make sure this folder contains required files. In case you needs to restore earlier backup, you have to manually keep older backup files to Internal storage/MyEFS folder. TO RESTORE backup you need to LONG PRESS restore icon. (to prevent accidentally tap)

Note : This application is not for just playing around, DON'T restore just to check/test application, Restore option must be used only when you really needs it.
If you don't know what is EFS and why you needs to restore, Don't use it. Read XDA thread for further info.

https://forum.xda-developers.com/galaxy-note-8/how-to/guide-how-to-root-note8-efs-backup-t3677038


We can't guarantee this will surely works on every case, you can use at your own risk. Also note that you can restore only backup which you have made on same device only.