IN THEORY for a normal installation, you need to boot to a live USB of Manjaro (in UEFI mode if that is your case, which I suppose it is), and restore GRUB. Once you are on the Manjaro live USB session, open a terminal, and chroot your Manjaro installation
manjaro-chroot -a
select your installation when prompted, and then reinstall GRUB (the two commands here are for UEFI installation which I guess you have)
grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=manjaro --recheck
grub-mkconfig -o /boot/grub/grub.cfg
Then exit the chroot to unmount properly your system, and reboot
exit
reboot
When rebooted, issue the following command to make sure GRUB menu entries are correct
sudo update-grub
BEWARE: you changed your GRUB config file from Windows, so now your GRUB will not be as before (but you can track what you have changed and reverse, and then issue another time the sudo update-grub command again).
Here is documentation GRUB/Restore the GRUB Bootloader - Manjaro
Maybe things could be different depending on your installation/setup of dual boot, so don’t take my explanation for granted. Not sure how you have setup your dual boot.
PS: this will happen every time you update your BIOS, it will erase some stuff in the motherboard, and will not automatically recognize a Manjaro installation so you will need to restore GRUB after BIOS update.