Grid page template question

I discovered this code https://wordpress.pastebin.com/CLYY2Y65 while searching for info on how to show posts in a two column format.

It works great, but it displays the posts in this format.
Post #1 | Post #4
Post #2 | Post #5
Post #3 | Post #6

I need it to display them in this format.
Post #1 | Post #2
Post #3 | Post #4
Post #5 | Post #6

You can see what I mean here, test post 9 being the newest 1 the oldest.
https://zeaks.org/test2/?page_id=2
But I have no idea how to do it, I don’t know very much about php. Any help appreciated, thanks.