https://phoenixnap.com/kb/grub-rescue
1. When the live system boots up, connect to the internet.
2. Open the terminal and type the following command to add the repository for the Boot Repair tool.
sudo add-apt-repository ppa:yannubuntu/boot-repair
Adding the repository for the Boot Repair tool.
Press Enter and wait for the repository to be added.
3. Update the repositories.
sudo apt update
4. Install the Boot Repair tool.
sudo apt install boot-repair
5. Start the Boot Repair tool via the terminal.
boot-repair