When you create a session, you can choose to make it a Self-Assign session. The first shopper who applies will be automatically assigned the shop, saving scheduler time.
Follow the usual steps for creating a Session, and in the Session settings, choose "Make these self-Assign shops (first applicant gets shop)
You can limit each shopper to a certain number of shops for the session--for example, you can enter "2" and each shopper may only take 2 open shops from this session.
All of the other session settings apply as usual.