On Cloudify, the deliveries are managed by the Admin and not the store owners.
You can pre-assign the delivery guys to the store by going to
Admin Dashboard > Users > Delivery Guys > Manage Delivery Stores
Then select the store you want to pre-assign to the selected delivery guy.
In this way when the order is accepted by the store, it will automatically be assigned to that delivery guy.
If multiple delivery guys are assigned to the same store, then all the delivery guys will get the order, and the first one to accept the order will have to fulfill the order.
Now coming to assign the delivery guys manually, this can only be done from the Admin Dashboard.
Goto Admin Dashboard > Orders > View any order > On the right-hand side, you can see the Assign Delivery Guy option.
On the admin dashboard, this feature is provided so that Admin can assign/reassign delivery guys manually.
The recommended flow is still pre-assigning the delivery guys.