How do you avoid keyword cannibalization in ecommerce?

so I am currently ranking my shopify store, and as my keywords bounce around I have noticed sometimes my highest ranking page for a keyword goes like this:

www.mysite.com/collection/green

But I want the following url to rank: www.mysite.com/collection/

The former page is created by shopify for products that come under a certain tag. EG green

how do I show google I only want to rank for the collection page?

Hope that makes sense, and thank you in advance.