Hi @nailinbaker,
Unfortunately Square doesn't allow editing of the SMS notifications, but you can definitely edit email templates (many of which are also sent at the same time as SMS).
Using a computer, login to your dashboard, go to Appointments > Settings > Communications. Down the bottom of this page under the different settings is where you can edit the templates Square is using for emails sent to your customers.
My recommendation is making sure whatever you do, make your words snappy and clear so it's really easy for customers to get the key points from a quick open (we have used this to overcome a few late arrivals where they didn't read our earlier info about parking etc).
Hope that helps!
