To edit GRUB configuration open config file located at /etc/default/grub
/etc/default/grub is a configuration file used by the GRUB bootloader on Linux systems. It contains various settings that can
be used to customize the way the bootloader behaves.
GRUB_DEFAULT is a setting that determines the default operating system that will be booted by GRUB if the user doesn't make a
selection during the boot process. This setting can be set to a number of different values, depending on how the operating
systems are listed in the GRUB boot menu. For example, if the first operating system listed in the boot menu is the one you want
to boot by default, you can set GRUB_DEFAULT=0. If the second operating system listed is the one you want to boot by default,
you can set GRUB_DEFAULT=1, and so on.
GRUB_TIMEOUT is setting that determines how long GRUB will wait for the user to make a selection during the boot process
before it automatically boots the default operating system. This setting is specified in seconds. For example, if you set
GRUB_TIMEOUT=5, GRUB will wait for 5 seconds for the user to make a selection before automatically booting the default
operating system. If you set GRUB_TIMEOUT=0, GRUB will not wait at all and will immediately boot the default operating system.