when you run sudo apt update and you see a package repository name which is for an uninstalled application or package in your ubuntu machine you have options .

/etc/apt/sources.list.d/ directory

navigate to this directory :

cd /etc/apt/sources.list.d

then find the package name with find :

sudo find ./ -name '*package_name*'

and after this :

sudo grep -r 'package_name'

and just BECAREFUL ! and CAREFULLY remove those files .