It's actually quite simple. You will need a keyboard and mouse. Usb or airmouse one.
- Use the browser and go download the apk you want to install. Sites like apkpure or apkmirror work best.
- Try to download as usual until you get the "Sorry" error.
- On the page you're on should be a link for failed downloads.
- Use mouse and long click on it.
- On the menu that appears choose Save link. You should see Starting download appear briefly on screen.
- Now, using the keyboard hit Ctrl+J and you will get the stock droid Download Manager.
- Wait for download to finish and click on whatever it is you downloaded.
- A familiar app install window should appear. Rest should be self explanatory.
Rinse and repeat.

Do note that installing just the playstore apk doesn't do jack. It won't open. Working on figuring that one out..
Hmmm. Then that update.zip might be gapps along with some other hypptv stuff. Gonna need to get one to test after rooting this box and replacing the recovery.img.. Thanks bro.

Power off and back on.. Try again. Steps are accurate.

Yes, long click the link about failed downloads..
I'm away and can't verify current firmware version but it's the latest and if the trick worked for me and others.. Should work for you too.

You are doing it wrong.. Instructions said "On the page you're on should be a link for failed downloads." Didn't say at the top or address bar, etc. Of course you click there it'll ask if you want to copy. You are supposed to look for the provided link for failed downloads.

Now, from your picture, do you notice the part that says.. "If the download doesn't start.......". You know what to do.. Follow the instructions.

Edit: FYI, I suggest you install a file manager first and then can easily install apks later. Apks can be downloaded via pc, copied and plugged in. Also, just get the official Kodi from the official website or install SPMC instead.

Good.. Now follow the rest of the instructions. Next step says to use a keyboard..