Once the admin user logged into the system, on the left top of the screen admin user will find a list of the menu from that Click on Administration TAB
On the left panel, the admin user will find a list of the folders hierarchy select user administration under that by clicking the user list admin user will get the list of users in the system.
In the search box, search the locked user in the system
Note: The red color lock symbol indicates that the user is locked out of the system.
Click on the Red highlighted lock button to unlock the user.
Note: The Black color lock symbol indicates that the user is unlocked in the system.