When importing new Orders – if you need to generate the Order Name from Shopify, just leave that Name column blank (or don’t have it in the import file at all).
That will make the Matrixify App generate your Order Name automatically incremented by Shopify.
To set the boundary where the next Order begins across many rows, use the Number column. For the same Number, the rows will be assigned to the same Order, and the next Order will start when the Number value changes.
Read more in the Orders sheet documentation.