Find ^Line\h+(?=\d)
Replace Line
Again, search mode is Reg Exp

yes, @Alan-Kilborn 's suggestion seems to be the best and easiest way to do so.

if you need help on the column editor:
once you’ve run alan’s regex with “replace all”, hold the [alt] key and mark (draw) a cursor-line from the end of the first word Line to the end of the last word Line like shown at the screenshot below.

then open column editor, select number to insert, with initial number 1 and increase by 1, and hit ok.

after that, you list will look like this.

I would do:

Find: ^Line\d+-\d+
Replace: Line
Search mode: Reg Expression

Then, follow that up with inserting a column of ascending digits (see the Column Editor on the View menu).