An age-old question appearing from time to time, is: 'How do I change the order of my posts?'
The answer has always been the same - edit the post's date in the Post Editor - manually, individually.
Why? Well, Blogger is dynamic - that means, inter alia, that it displays the latest post first. To change that, you have to do it manually, individually, in the Post Editor.
Now, recently, as you'll see in the above Blogger Help Forum link, some Bloggers suggest changing the blog Archive option "Show Oldest Posts First". That's great - but - only for the Archive Display sequence.
It won't change the order of your blog posts on your Main Page!
So, albeit a very exhausting process, the only way I know of, to change the sequencing of dates, on posts, is to do it individually, and manually. Here, in the next image, is where it is done...
Sorry - there's no short-cuts! Hopefully, the kids at Blogger will find a way, soon.