Embed code with reference from two collections

Hi guys,
i’ve got the following problem:
I have a custom code embedded in a Dynamic Page. Inside it i have javascript which main function is to sum values from two parameters. The problem is that the first value is picked up from a field of the current dynamic collection, but the other value is set inside another collection and it seems that I cant add this value inside my custom code via +Add Field button since the system doesn’t reffers to other collections. I tried to put Dynamic List and set it to the second collection but then +Add field doesn’t reffers fields from the current collection…

How to set those two vars from fileds of two different collections?

Here is my public share link: https://preview.webflow.com/preview/mcottage?preview=8533533f3e712fa84dc9377c77007fbf