You can configure the discount offer using different types: Variant, Product, Collection, and Cart. You need to select the type to apply the discount offer.
Variant: You can provide a discount offer on the product’s different variants. You will see the two options by clicking on the “Variant”.  To apply the discount offer for all the variants, click on the Select All option. But, if you want to apply the discount offer for the selected variant only, click on the Custom Selection option. By clicking on the “Custom Selection” option, you will see the + Add Variant button. 
By clicking on the “+ Add Variant” button, you will get the popup of the products’ variants. You can select the specific variants on which you want to apply the discount offer. After selecting the variants from the popup, click on the Add button.  The selected variants will be listed. 
You can search any variant by inserting the variant name in the “Search Variant” text box. You can remove all the selected variants by clicking on the “Remove All” button. If you want to remove the specific variant, click on the ‘delete’ icon of that individual variant.