How Do I Delete Multiple iMessage Conversations At a Time?

I am trying to delete multiple text messages at one time (i.e., I’m referring to multiple separate messages from different senders, not multiple messages within a single conversation stream). Pressing CTRL doesn’t allow me to select multiple separate messages (conversations). I can only laboriously delete one message (conversation) at a time. I can’t find a workaround and no technique in online forums seems to help. Is there a way to delete multiple text messages at once?
Periodically, I want to clear my iMessage list of unwanted or completed text conversations. I want to do this efficiently — not one conversation at a time.
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Philip