Once you have installed RebornOS, you may see that there is no Windows entry present in Grub. You can restore it by following the below steps:
Install os-prober and ntfs-3g if not already present.
sudo pacman -S --needed os-prober ntfs-3g
Run os-prober to check if it recognizes Windows
sudo os-prober
Permit grub to use os-prober
sudo pacman -S --needed gedit
sudo nano /etc/default/grub
Uncomment/edit/add this entry:
GRUB_DISABLE_OS_PROBER=false
Make sure that there is no
#before the entry.
Save the file and exit(Control S, Control X).
Regenerate grub entries
sudo grub-mkconfig -o /boot/grub/grub.cfg