When creating or editing an issue, you can automatically assign it to a user of your choice by setting an area for the issue.
To do this, you first need to select an area owner for that area.
Go to the Settings page of your project and select 'Areas' from the Issue management dropdown menu
Click on an Area in the list or click the 'plus' button to add a new area.
Select the “Area owner” from the drop-down list
Click on Save.
From this point onward, any new or edited issue for which the area has been chosen, will be assigned to the area owner if not an other specific user is assigned.