You have a hybrid Azure Active Directory (Azure AD) tenant. You plan to deploy an Azure Virtual Desktop personal host pool. The host pool will contain 15 virtua...

Configure direct assignment.
Unlike automatic assignment, when you use direct assignment, you must assign the user to both the personal desktop host pool and a specific session host before they can connect to their personal desktop. If the user is only assigned to a host pool without a session host assignment, they won't be able to access resources and will see an error message that says, "No resources available."
To directly assign a user to a session host in the Azure portal:
1. Sign in to the Azure portal.
2. Enter Azure Virtual Desktop into the search bar.
3. Under Services, select Azure Virtual Desktop.
4. At the Azure Virtual Desktop page, go the menu on the left side of the window and select Host pools.
5. Select the host pool you want to assign users to.
6. Next, go to the menu on the left side of the window and select Application groups.
7. Select the name of the app group you want to assign users to, then select Assignments in the menu on the left side of the window.
8. Select + Add, then select the users or user groups you want to assign to this app group.
9. Select Assign VM in the Information bar to assign a session host to a user.
10.Select the session host you want to assign to the user, then select Assign. You can also select Assignment > Assign user.
11.Select the user you want to assign the session host to from the list of available users.
12.When you're done, select Select.
Reference:
https://docs.microsoft.com/en-us/azure/virtual-desktop/configure-host-pool-personal-desktop-assignment-type