Thank you for your question.
There is a standard query that wil show you patients who have attended an appointment in the last xx months which you can edit to suit your requirement.
Thank you for your response. Now that I have created the query and I have list of patients how do I send them all a text message? Do I have to do mail merge and than choose the right message? I would be grateful if you could help me with that.
Yes you can use the Mail Merge feature to send them all a text message. The following link includes a Job Aid that shows you how to send messages using Mail Merge.
Yes, if you left click and highlight all the names in the list. Then click Mail Merge. Click Yes to the prompt that appears and simply select the SMS you wish to send. (See pic)
If you don't already, you will need to create your SMS message within Document Manager.
Hope this helps.