In order to assign the ticket to another user, you need to open the ticket.
On the upper right corner select the folder that belongs to this user. You can also select priority.
If you want messages of a specific category to come to a specific user, then this must be configured in the Rules tab.
First, you should give the user access rights to the folder where messages will come.
Then you will need to set up Rules in such a way that, for example, tickets from one marketplace come to the user's folder.
To do this, go to the menu, select the Tools tab, then the Rules tab.
Click the “Add new” button and enter the necessary information: