Follow these steps to write a pre-set text message to your NFC tag.
Open the NFC Tools app. From the main dashboard, tap the Write button (the orange icon with a downward arrow).
Inside the Write menu, tap Add a record. This will open a list of different data types you can write to the tag.
Scroll down through the record types and select SMS. This is perfect for things like pet collars or lost-and-found items.
In the "To" field, enter the phone number you want the message to go to. In the "Message" field, type your custom text (e.g., Hi! I found your pet!).
Tap the Checkmark in the top right corner when finished.
You will see your record listed. Tap the Write / [X] Bytes button. A "Ready to Scan" dialog will appear.
Hold the back of your phone near the NFC tag. Once the app displays a green checkmark, your tag is successfully programmed! When scanned by a smartphone, it will now automatically prompt to send that SMS.