Fetch Doctype into new doctype

How do we fetch data as in entire data list from one doctype in to another doctype ?

What I am trying to achieve is:

I have customer list in my CRM and I have created a new doctype “technical”, now I want to fetch data from existing customer list of CRM to the new doctype “technical” with only few custom fields of customer list.

You can add a “Link” field in your DocType to get all your customers. It will also take you to that customer if you click on it.

That will only fetch the customer list when I make a new doc. But I want to fetch all the docs from customer list and list here in “technical” as well but will not print few fields when clicked on it.

any help ???

you can see this for reference: