Follow these steps to split or move products from one sale to another.
Go to the sale you're working on
From the list of items in the sale, select the products to be moved. If there is more than one product you can use the chevrons to adjust selected quantities within a row
Tap the three dot (...) menu
Select 'Move to sale' with the arrow button to move the selected products
Select an existing sale (you can peek into the sale with the eye icon) or create a new sale
Tap 'Move' to move the products across
For more information, watch this video: https://youtu.be/cD6jKfyNNyw