showing VAT and non VAT (Strikethrough price)

[Eugene13]

Hi. I just want to know how we could show the including price (strikethrough) with the variations clicked. we downloaded an app with variation but once we click the variation, the including price (strikethrough) is gone. we can't use the built-in variation of Shopify as we are taking too much time on that. any help on this? thankyou!