There is nothing built into ACF that will do this. You would need to do your own custom JS https://www.advancedcustomfields.com/resources/adding-custom-javascript-fields/.
While you might want this done in the admin the better solution is to use css text-transform on the front end. The only reason I can see for enforcing upper case in the admin is because that’s the way you want it shown on the front of the site.
If you cannot edit the CSS file in your theme then you could also use an acf/format_value filter to apply strtoupper() to a specific field.
