Installing apps with new Apple ID password

I recently changed my Apple ID password to secure my account from possible hacking. When I did this, I decided to delete Facebook and Facebook Messenger from my iPhone because I suspected a possible breach. After changing the Apple ID password, my iPhone 6 continually asks for the password which is fine, but when I input the correct password I cannot reinstall Facebook Messenger. I use Fingerprint ID, too and never had I had an issue with installing apps prior to the change of the Apple ID password.

When I use the new password on my MacBook Air, I have no difficulties. When I used the password on my iPhone 6 to update apps like iTunes, I had no difficulty. When I tried to make a purchase of Quickbooks Self-Employed, I again encountered an error with the new password, even after verifying the purchase with my fingerprint.

The next step I tried was to find out how to install an app onto my iPhone 6 by using my MacBook Air while the phone is connected (by USB) to the laptop. I do not know how to install apps to my iPhone from my laptop while logged into Apple (up until now, I have been primarily a PC user).

So, my question is in two parts:

1. What do I need to do after changing an Apple ID password so that I can make purchases or verify app downloads? I.e., my iPhone comes up with "error" when I input the new password correctly and use fingerprint ID verification while trying to reinstall Messenger and making a purchase (of Quickbooks Self-employed by Intuit).

2. How do I download apps onto my iPhone 6 by using my Apple ID online from my MacBook Air? I have sharing enabled and am connected via USB.