Is it possible to delete an unread text that I sent on iMessage?

Hello!

Only if it was sent with iMessage. If the message is blue, you can un-send it. Long hold the message, and tap “Undo Send.”

Note: You only have two minutes to un-send a message, and you have 15 minutes to edit it, which can be done up to 5 times. If the Undo Send option is gone, edit the message and just put a “.” so there is some text, but your original message is gone.

See: Unsend and edit messages on iPhone - Apple Support

Have a great day!