Changing the display order of your Shopify product variants is quite simple using Mixtable's Excel-like spreadsheet. The display order of your variants is stored in their position field. Every variant of your product has a value in its position field, and Shopify orders the variants on your product pages based on the value of this field.
So, to change the display order of your variants you need to map a column to the position field on a worksheet that syncs your store's variant data.
Now that you have the position field mapped to a column, changing the values of cells and clicking the Done Editing button will sync those changes back to Shopify. It's up to you how to change the cell values as, depending on your process, you have a few options.
You can manually change some variants' position in order to force a particular variant to show up at the top. This can be your best seller, for example.
You can also use Mixtable's sort functionality to rearrange the rows in the variants-syncing worksheet based on some logic. Then update the position cell values after the sort is done with the order of the rows. You can do this manually, or by dragging cell values as you can in Excel. You can also use the Excel ROW() function to populate the cells with their current row number.