First you should upgrade your machine to PHP 7.4, it you haven't checkout this great guide from Brent
the short version is to do these steps using homebrew:
Update Brew
brew update
Next upgrade php
brew upgrade php
At this point your machine should be using PHP 7.4 but Laravel Valet may still be using PHP 7.3.
Upgrade Valet:
Update composer
composer global update
Next update Valet
valet install
Now to tell valet to use the latest version of PHP
valet use php
this tells valet to unlink php 7.3 or whichever version you have and use the latest version i.e 7.4
Or you can specify the version to use:
valet use php@7.4
