It is generally easier to import multi-variant listings but if you only have a few multi-variants and have already imported products as none multi-variants you can convert products into multi-variant products inside Xpress Lister.
1) Click Add in the header row
2) Click Create Multi-variant Listing
3) Populate the Create Product (Multi-variant Listing Creation Tool) screen. The example below shows creating a T-Shirt in various sizes.
4. Click Create these Variants. You will see the following:
5. Set the Stock Level and Price for each variant