Using Edit>Replace, enter either ^p or ^l in the Find what control and put a
space in the Replace with control.

Whether you need the ^p or ^l will depend on whether each item is in a
separate paragraph, in which case the line will terminate with a ¶ when you
click on the Show/Hide button on the toolbar (the one with the ¶ icon).  For
that case, you would use ^p.  If each line does not terminate in a ¶, use ^l