How can I find and replace # with a symbol?

I have written a story using the # symbol as a scene separator. I am trying to find a way to replace the # with a dingbat without having to find each # and replace it manually. Even if there is no way to do a Find All and Replace All, if I could just Find Next and then use Ctrl+V to manually insert the copied dingbat, that would speed things up considerably, though obviously if I could do a Find/Replace All in one go, that would be preferable.

You didn’t say which version of LO you are using.

In v5.4.5.1 (and many others), go to Menu Edit → Find & Replace. Enter the Find character, enter the Replace character, then click on Replace All. Is that not what you want?