All you need to do is a create a rule.
When setting up, select “receiving SMS”.
You can select to mark as read only SMS coming to Shared Numbers or a particular dedicated number of yours. If you want to mark inbound SMS regardless of the number they are being sent to, pick “Any Number”.
You can then enter as many keywords as you please if you only want to mark only particular SMS depending on the keyword(s) they contain. If you would like all incoming SMS to be marked as read regardless of keywords, leave these boxes blank.
Go to the next step, and select “Mark as read”.
Click Save Rule and… Happy days! All incoming SMS that meets your rule will be marked as read in your inbox.