When product-id 2000 is in cart, then on checkout page

Hi support,

I have bought your product today on your recommendation.
However I cannot so far get the plugin working the way I want to.

Link to website: https://orden.dk

RULE
When product-id “2000” is in cart, then on checkout page show countdown timer for promotion of product-id “2788” (having 50% discount).

How do I choose these products and make this rule?

Thanks.

/Tommy