Keyboard top row not working properly - need volume app for workarounds

I have a Macbook Air 11 i7 8GB from 2015 and the top row of the keyboard is not working properly. That issue has been discussed in other threats but none of the solutions worked for me. Neither did the technician from the Apple found a solution apart from changing the top case of the keyboard which costs more than the value of the Macbook is. So I found an app in the Apple Store, called Brightness Slider. After installing it, it let me assign the functions 'brightness up' and 'brightness down' to certain keys of my choice as a shortcut. And I tried to assign them to the original ones, F1 and F2. And surprisingly now it works perfectly. As I am working with video, to have back a brightness control it's half of the problem resolved. But I need the same thing now for volume control. Anybody knows an app that controls volume? I only found these apps, they are multifunctional for several apps, mixing boards EQ, etc and without the possibilitiy to assign shortcuts. And this it what I need. Any help very welcome. Cheers!