In the new issue view, there's no button Assign as the old view use to have.
Add the button (or an option) to have a screen to assign the issue for a user.
On this screen, the user can perform an assign and add comment at the same time. This important because some times you need to assign the ticket and leave information during this action. Without this button, we need to do two actions.
Create a transition from any status to itself with a screen that has the assignee field.