After you enable an LRS account in Lync, you can assign a Lync Online (Plan 2) or Lync Online (Plan 3) license by using the Office 365 administrative portal. You can also use Windows Azure Active Directory Module for Windows PowerShell cmdlets to assign a license. Go to Users and Groups, select the LRS account, and assign a license as follows:
After you assign a license for Lync Online, you will be able to log into this account by using any Lync client. You can perform a validation by using a Lync client.