Delete messenger texts

[nickcoff]

When I exported my Samsung S7 to my new S9+, all my messenger texts are single texts from the same people instead of combining one person's messages in a single file.
Obviously, this is taking a lot of room and memory. But the only way I can find to delete them is to select each message separately.
Please tell me there's a simpler method, lol. I've got >5,500 messages. Of course, I don't need every message but I spent a 3 hr flight deleting when there were >8,000 and I've still got 5,500. Ugh!

 

[webworkings]

If you are talking the phone's messaging app, you should have the option to delete them all at once. If you are talking a specific app on the device (other than the phone's original messaging app) then you would have to look for the same in that app. They are all set up differently.