Delete messages that weren’t supposed to be deleted

What do you mean by "top conversations?" Do you mean "pinned conversations?" If so, see the instructions in this article:

Keep track of messages on iPhone - Apple Support

Or, do you mean you deleted messages? If so, whether or not you can get them back depends on several factors. Start here:

Recovering deleted texts and iMessages - Apple Community

This comes down to only one thing: what is your iOS?

answer that question and you will have your answer.