$REMOTE_URL is the location to which you want to push to (replace
$REMOTE_URL with an actual URL), then, for an existing remote—as indicated by
$REMOTE_NAME—you would invoke the following command:
git remote set-url --add --push $REMOTE_NAME $REMOTE_URL
For me, I usually set
$REMOTE_NAME to just
origin. But of course, for various reasons, you can choose an entirely different remote name.