Alon Gal's notes

https://getgrav.org/blog/macos-mojave-apache-multiple-php-versions
https://stackoverflow.com/questions/40276967/uninstall-laravel-valet
https://laravel.com/docs/5.8/valet#installation

First make sure you have the php version you want to switch to

brew install php@7.2
brew unlink php@7.1 && brew link --force --overwrite php@7.2

Second, make sure you updated valet to the latest version.

sudo brew services stop nginx
sudo brew services stop dnsmasq
sudo brew services stop php@7.2
composer global remove laravel/valet
sudo rm -r ~/.valet
rm /usr/local/bin/valet

Now you can re-install valet and configure it to the new php

composer global require laravel/valet
valet install
valet restart
valet use php@7.2
valet use php

To check what php version you have installed

brew search php

To switch php version 7.2 back to 7.1

brew unlink php@7.2 && brew link --force --overwrite php@7.1