How to remove offending key in git when you try to push your changes?

It says:

Offending key for IP in /home/alireza/.ssh/known_hosts:10

So for some reason you have to delete 10-th line in known_hosts.

Run this command to delete 10-th line in known_hosts:

sed -i '10d' ~/.ssh/known_hosts

Or use ssh-keygen

ssh-keygen -R git.mywebsite.ir

Quote from man

 -R hostname
         Removes all keys belonging to hostname from a known_hosts file.
         This option is useful to delete hashed hosts (see the -H option
         above).

When I got the messages:

Offending key for IP in /home/myusername/.ssh/known_hosts:12

Notice the line number - in my case - 12

So open 'known_hosts' file and delete the 12-th row.

For me this solved the problem.

P.s. Notice if you cannot find the .ssh folder - the .ssh folder is hidden and in order to see it from the file manager - you have to "Show hidden files and folders". In Linux Mint (and possible in your distro too) when in the file manager - there is a shortcut to show/hide hidden folders -> Ctrl+H

Cheers