The win2grub way: One command. Restart. Linux.
# save as `to-linux.bat` @echo off win2grub --set-next \EFI\ubuntu\grubx64.efi shutdown /r /t 5 (Runs the command and restarts in 5 seconds. Cancel with shutdown /a ) Did you accidentally delete GRUB? No problem. win2grub can also set Windows Boot Manager as the default:
The old way: Save your work, restart, spam the Shift or F12 key, select the boot device, wait for GRUB, then select Linux.