SOLUTION!!! OF HOW TO FIX THE APP NOT INSTALLED PROBLEM!!
I'm so excited and happy people. I have spent 3 days trying to figure out how to fix 'App not installed' problem. I found a solution. Since, I have to use a android tablet because my laptop has gone out of usage and I lost my phone. But anyways, this is how I fixed the problem (I don't know if it works for everyone). Go to settings and go to 'apps' all should show and go to each app that you use all of the time and show info and clear the cache of all the apps you have to do each one and then download the mod again and it should install this worked for me :)