use this code from dialer *#87976633 and long press # key for 2-3 seconds. then restart the device. please backup your data before doing it. it might hard reset your handset resulting in losing your data.
Install and Open “ES File Explorer” and press on the top left icon
Go to Tools and turn on “Root Explorer”
Go to Local > / Device > efs > FactoryApp and open factorymode as text in “ES Note Editor”
Change it from OFF to ON and save it
Open keystr as text in “ES Note Editor”, change it from OFF to ON and save it
Reboot
Strange that your S10+ is rooted be careful as your knox may be tripped. you would loose your warranty and phone OR
You can alternatively exit the factory mode on unrooted device Simply go to Settings > Application Manager> All Search Factory Test and proceed to ‘Clear Data’, ‘Clear Cache’
OR
The factory mode can be activated when the EFS partition is corrupted in the event one installs custom ROMs or bad mods, downgrades the current system version.
So if you were trying to install the stable version via recovery??
