Kits in SKULabs are originally created out of items. When a listing sync is run, it will automatically build an item first, from which you can then convert into a kit. If you are looking to change a kit back into an item SKU, here's how:
To recreate a Kit as an item SKU:
Delete the kit, (component items will not be affected)
Create a new item for that SKU (Inventory > Items > New Item)
Manually link the item to its listing.
Alternatively, depending on your stores setting, you could also simply run a listings sync to reimport the listing, thus automatically building and linking the item automatically.
Please contact SKULabs support if you have additional questions on this.