Add to sources.list
Open the sources.list using your favorite text editor,
su
mousepad /etc/apt/sources.list
Delete or comment out the existing repository details in the file. Copy and paste the following content into the file.
deb http://debianmirror.nkn.in/debian/ buster main
deb-src http://debianmirror.nkn.in/debian/ buster main
deb http://security.debian.org/debian-security buster/updates main
deb-src http://security.debian.org/debian-security buster/updates main
# buster-updates, previously known as 'volatile'
deb http://debianmirror.nkn.in/debian/ buster-updates main
deb-src http://debianmirror.nkn.in/debian/ buster-updates main
Update the repository list and upgrade the packages
apt update
apt upgrade
