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Trouble with apt update




Hello all,
    When I run the command: sudo apt update
I get this error:
$ sudo apt update
Ign:1 http://debianmirror.nkn.in/debian stretch InRelease
Hit:2 http://debianmirror.nkn.in/debian stretch-updates InRelease       
Hit:3 http://debianmirror.nkn.in/debian stretch Release                       
Hit:4 http://security.debian.org/debian-security stretch/updates InRelease    
Ign:6 http://ppa.edx.org stretch InRelease                                    
Err:7 http://ppa.edx.org stretch Release      
  403  Forbidden
Reading package lists... Done
E: The repository 'http://ppa.edx.org stretch 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.


Can someone help me out.
Thank you