Verified answer

If you have made a working screen lock app you can just install the apk on your phone

You can also change the type of screen lock used in settings in the security menu

You could also download a 3rd party screen lock from the play store or other source and install it on your phone

If installing your own apk or one from a source other than the play store you will have to ensure 'unknown sources' is ticked in the security section of your phone settings

Here is the list of Best Android Lock Screen Apps -