Use the Shortcuts app to create a personal automation
Open Shortcuts and tap Automation
Tap Create Personal Automation
Choose Time of Day
Set the date and time
Tap Next
Add the Send Message action
Enter the recipient and message
Turn off Ask Before Running if available
Tap Done
Use a third-party scheduling app if you need advanced text scheduling
Use your carrier’s messaging service if it supports scheduled messages
Set a reminder to send the text manually if scheduling is not available