As far as I know, there is no way to mark a text message as unread (if there is, please share!).
I often receive text messages at inconvenient times, read them quickly, and then forget to reply to them when I'm free. I'm looking for ways to simulate "mark as unread" (or "remind me about this text message") as easily as possible.
The best I have come up with it simply to not read the message in the messages app – then I can read the first sentence or so, get the gist of it, and I still have an unread notification on the app icon. But this is not ideal of course.
One thing that's an obvious suggestion but is just too clunky is to add a todo-list item to respond (just like I'd add any other todo item).
Best Answer
There's technically no way to mark a message as unread, but there's sort of a hacky workaround way to simulate it.
Hold down on the message you want to mark as unread and click "copy". Then start a new message, address it to yourself, paste in the message and send.
Since there's a slight delay, you can back out of the conversation, and you will have 1 unread message from yourself.