Which theme you are working? and what you want from this field?
Hi @JeroenHes ,
as JoesIdeas noted you cannot change the check out process if you are not in the Shopify Plus program. If I recall it correctly also the Shopify terms of service forbids such adjustments.
Check your checkout form options
You can change some of the fields on your checkout pages so that they are required, optional, or hidden.
From your Shopify admin, go to Settings > Checkout.
In the Form options section, make the appropriate changes.