Copy it to the smartphone in the documents folder or another unprotected folder and open it with the preinstalled file explorer (total commander disabled installing apks, you need another total commander version from the website and not from play. Maybe you have to activate in the security settings first that unknown sources allowed.
But you can also use Google Play. You can try there the Beta Program of MFN.
I have at time 7.3.21 installed. 21 is more than 7 :)