How to "submit a flag for moderator attention"? Purpose: Delete a thread that has become futile meanwhile

I have started a thread some time ago, which topic has no meaning anymore.

Is there a way to delete the whole topic? The UI states that I could “submit a flag for moderator attention together with reasoning”. How do I do that?

Click the “…” next the :heart: and interlocking chain (to the left of the “reply” and it will reveal the “Flag” icon.