Delegated administrators can now manage the assignment of permission set groups for users in their delegated group, giving you more time for other admin tasks.
Where: This change applies to Lightning Experience and Salesforce Classic in Enterprise, Performance, Unlimited, Developer, and Database.com editions.
How: From Delegated Administration in Setup, create or select a delegated group. Then in Assignable Permission Set Groups, select the permission set groups that delegated admins can assign to users or remove. Delegated administrators can manage assignments for the permission set groups in their delegated group, but they can’t modify those permission set groups.
Allow Delegated Admins to Manage Permission Set Group Assignments (salesforce.com)