GPG Keyring error - DGX OS 5

Recently got DGX OS upgraded to DGX OS 5. Tried running sudo apt-get update and getting the below error:

adminuser2@dgxserver2:~$ sudo apt-get update
Hit:1 https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2004/x86_64  InRelease
Get:2 https://repo.download.nvidia.com/baseos/ubuntu/focal/x86_64 focal InRelease [15.5 kB]
Get:3 https://repo.download.nvidia.com/baseos/ubuntu/focal/x86_64 focal-updates InRelease [15.7 kB]
Err:2 https://repo.download.nvidia.com/baseos/ubuntu/focal/x86_64 focal InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 208CE844D9F220AD
Err:3 https://repo.download.nvidia.com/baseos/ubuntu/focal/x86_64 focal-updates InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 208CE844D9F220AD
Hit:4 http://us.archive.ubuntu.com/ubuntu focal InRelease
Get:5 http://security.ubuntu.com/ubuntu focal-security InRelease [114 kB]
Get:6 http://us.archive.ubuntu.com/ubuntu focal-updates InRelease [114 kB]
Reading package lists... Done
W: Target Packages (Packages) is configured multiple times in /etc/apt/sources.list.d/cuda-compute-repo.list:1 and /etc/apt/sources.list.d/cuda-ubuntu2004-x86_64.list:1
W: Target Translations (en_IN) is configured multiple times in /etc/apt/sources.list.d/cuda-compute-repo.list:1 and /etc/apt/sources.list.d/cuda-ubuntu2004-x86_64.list:1
W: Target Translations (en) is configured multiple times in /etc/apt/sources.list.d/cuda-compute-repo.list:1 and /etc/apt/sources.list.d/cuda-ubuntu2004-x86_64.list:1
W: GPG error: https://repo.download.nvidia.com/baseos/ubuntu/focal/x86_64 focal InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 208CE844D9F220AD
E: The repository 'https://repo.download.nvidia.com/baseos/ubuntu/focal/x86_64 focal InRelease' is not signed.
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.
W: GPG error: https://repo.download.nvidia.com/baseos/ubuntu/focal/x86_64 focal-updates InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 208CE844D9F220AD
E: The repository 'https://repo.download.nvidia.com/baseos/ubuntu/focal/x86_64 focal-updates InRelease' is not signed.
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.
W: Target Packages (Packages) is configured multiple times in /etc/apt/sources.list.d/cuda-compute-repo.list:1 and /etc/apt/sources.list.d/cuda-ubuntu2004-x86_64.list:1
W: Target Translations (en_IN) is configured multiple times in /etc/apt/sources.list.d/cuda-compute-repo.list:1 and /etc/apt/sources.list.d/cuda-ubuntu2004-x86_64.list:1
W: Target Translations (en) is configured multiple times in /etc/apt/sources.list.d/cuda-compute-repo.list:1 and /etc/apt/sources.list.d/cuda-ubuntu2004-x86_64.list:1

I have tried deleting and upgrading key, but get this error:

adminuser2@dgxserver2:~$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 208CE844D9F220AD                      
Executing: /tmp/apt-key-gpghome.ToLR3OkPJK/gpg.1.sh --keyserver keyserver.ubuntu.com --recv-keys 208CE844D9F220AD
gpg: keyserver receive failed: No data

Kindly help : )

Please try the following instructions for rotating/updating the GPG keys on DGX.