Installing .zip file of platform-tools on Debian

I know I'm missing something really obvious here, but I'm banging my head against the wall trying to undo a very unwanted "update" that un-rooted my phone and I just don't have any mental energy left to figure out why I'm not succeeding in updating adb to the latest version. (It's an oldschool Pixel 1, with the a/b structure that older versions of adb can't fully deal with.)

What I'm trying to install on Debian is this:
https://dl.google.com/android/reposi...test-linux.zip

It downloads just fine, I can unzip the file just fine, but -- then what? If I type 'adb' I get my old version.

Thanks in advance, I know it's a dumb question!