Don’t edit this manually…
Just do as you asked about earlier:
- Format the partition (for example as
ext4) - Run
sudo update-grub - Reboot.
It doesn’t get much easier than that.
I believe OS-Prober is enabled by default in recent KDE versions, so you shouldn’t need to worry about that. But, just in case… check that it’s enabled in /etc/default/grub, as @Aragorn mentioned.
Look for a line that contains GRUB_DISABLE_OS_PROBER=false and make sure it’s uncommented.