regex - How do I combine that

Question

I have these texts:

1000
2000
3000
4000
5000
6000

Now I want them to be like that but each one in a single line not all in one line, like in the picture:

1000:2000
3000:4000
5000:6000

Answer 1

You can use following regex (tested on VSCode)

^(.*)
(.*)$

and replacement text as

$1:$2