I installed Valet for the first time and I had some problems listed below:
Unable to determine linked PHP.
An official response here: https://github.com/laravel/valet/issues/341#issuecomment-287048987
valet uninstall
sudo brew services stop nginx
sudo brew services stop php70
sudo brew services stop dnsmasq
brew uninstall nginx
brew uninstall php70
brew uninstall dnsmasq
rm -rf ~/.valet
rm /usr/local/bin/valet