Please try the following troubleshooting steps:
1) Open a bash or Git Bash shell on your machine.
2) Find the hostname or IP address of the server on which your remote Git repository is hosted.
3) Run the following command in your bash shell to determine if you already have an entry for the server's key fingerprint in your "<HOME>/.ssh/known_hosts" file.
$ ssh-keygen -F <hostname>/<ip address>
where <hostname>/<ip address> is either the actual hostname or IP address you found in step 2).
e.g.
$ ssh-keygen -F github.com
3.1) If you do not see any output, then you do not have an entry for the server in the known_hosts file.
Proceed to step 4.
3.2) If you do see output from this command, verify whether the output matches that of the following command.
$ ssh-keyscan -t rsa <hostname>/<ip address>
e.g.
$ ssh-keyscan -t rsa github.com
If the output is different, then you need to add a new entry for the server to the known_hosts file. Proceed to step 4.
4) Navigate to your home folder, which should contain your .ssh directory. This is typically "C:\Users\<your-username>" on Windows and "~/" on Linux and macOS.
5) Run the following commands and verify whether the issue is resolved.
$ cd .ssh
$ ssh-keyscan -t rsa <hostname>/<ip address> >> known_hosts
e.g.
$ cd .ssh
$ ssh-keyscan -t rsa github.com >> known_hosts
NOTE: You should now see the proper output from the command in step 3.
