Assign to an user and only that user

Hi! I have a webform where I’m going to create some instances of a Doctype. With those created, I need to be able to assign them to specific users that will be using the webform in order to make that user (and only that user) able to see the doctype assigned.

On the sidebar I have all the available webforms that the user with an “investigator” (researcher in spanish) role can see. Every researcher is a different user. When I create an “Evaluaciones recibidas” (received evaluations) instance it has to appear only to the assigned user.

I hope I’ve explained myself right. Thanks!