rThe repository 'http://ppa.launchpad.net/danielrichter2007/grub-customizer/ubuntu focal Release' does not have a Release file

My Ubuntu version is 20.04, every time I try to sudo apt-get update it stops to show the errors like
"E: The repository 'http://ppa.launchpad.net/danielrichter2007/grub-customizer/ubuntu focal Release' does not have a Release file".

I have read in some other post(the link) that we have to delete some related config file, but how to delete it? Or can it be removed by just uninstalling grub and reinstall using
sudo apt install grub-customizer as mentioned in answer of question https://answers.launchpad.net/grub-customizer/+question/688951?
Please help with method to delete the config file as many say that its too dangerous to modify sources.list related files.
Please find the outputs for requested commands below.

sivakalyan@hsk:~$ uname -a
Linux hsk 5.4.0-33-generic #37-Ubuntu SMP Thu May 21 12:53:59 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

sivakalyan@hsk:~$ lsb_release -crid
Distributor ID: Ubuntu
Description: Ubuntu 20.04 LTS
Release: 20.04
Codename: focal

sivakalyan@hsk:~$ sudo apt update
[sudo] password for sivakalyan:
Hit:1 http://dl.google.com/linux/chrome/deb stable InRelease
Hit:2 http://in.archive.ubuntu.com/ubuntu focal InRelease
Hit:3 http://in.archive.ubuntu.com/ubuntu focal-updates InRelease
Hit:4 http://in.archive.ubuntu.com/ubuntu focal-backports InRelease
Hit:5 https://dl.winehq.org/wine-builds/ubuntu focal InRelease
Ign:6 http://ppa.launchpad.net/danielrichter2007/grub-customizer/ubuntu focal InRelease
Get:7 http://security.ubuntu.com/ubuntu focal-security InRelease [107 kB]
Hit:8 http://ppa.launchpad.net/fingerprint/fingerprint-gui/ubuntu focal InRelease
Hit:9 http://archive.canonical.com/ubuntu focal InRelease
Hit:10 http://ppa.launchpad.net/linrunner/tlp/ubuntu focal InRelease
Hit:11 https://download.sublimetext.com apt/stable/ InRelease
Hit:12 http://ppa.launchpad.net/teejee2008/ppa/ubuntu focal InRelease
Get:13 http://security.ubuntu.com/ubuntu focal-security/main amd64 DEP-11 Metadata [18.7 kB]
Hit:14 http://ppa.launchpad.net/ubuntuhandbook1/apps/ubuntu focal InRelease
Get:15 http://security.ubuntu.com/ubuntu focal-security/universe amd64 DEP-11 Metadata [31.6 kB]
Err:16 http://ppa.launchpad.net/danielrichter2007/grub-customizer/ubuntu focal Release
  404 Not Found [IP: 2001:67c:1560:8008::15 80]
Reading package lists... Done
E: The repository 'http://ppa.launchpad.net/danielrichter2007/grub-customizer/ubuntu focal Release' does not have a Release file.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

sivakalyan@hsk:~$ grep daniel /etc/apt/sources.list /etc/apt/sources.list.d/*.list
/etc/apt/sources.list.d/danielrichter2007-ubuntu-grub-customizer-focal.list:deb http://ppa.launchpad.net/danielrichter2007/grub-customizer/ubuntu focal main
/etc/apt/sources.list.d/danielrichter2007-ubuntu-grub-customizer-focal.list:# deb-src http://ppa.launchpad.net/danielrichter2007/grub-customizer/ubuntu focal main

And also yes, I made Windows as default in grub menu.
Thank you.