First, find zipalign.
find ~/Library/Android/sdk/build-tools -name “zipalign”
Copy the most recent build tools version, e.g.
/Users/me/Library/Android/sdk/build-tools/28.0.2/zipalign
Add it to /etc/paths.
nano /etc/paths
(Paste the zipalign path)
Save and exit ctrl+o, ctrl+x
Close the command window.