May i know how to add an admin credential to slim framework web application or edit a previous one
Slim does not come with any authentication package, however there are many you can implement. The package you implement will depend on your needs. If something basic from the browser you might try tuupola/slim-basic-auth. I use auraphp/Aura.Auth for a few of my projects. From an API you might want to look at something like thephpleague/oauth2-server.
Thank You for ur feedback