Create an ssh key if you don't already have one using ssh-keygen. Let's name it id_rsa_user.
Add the public key (id_rsa_user.pub) to your git service - bitbucket, gitlab, github, etc.
Enable the ssh-agent service in windows.
I've set mine to automatic - delayed start.
Move the your private key (id_rsa_user) to c:\users\<user>\.ssh
In the same folder, create a file called config with no extension. Populate it with the following:
Change your git service hostname as appropriate.
ssh push should now work.