We can sort the lookup field value using Workflow in Zoho Creator. Here ,we used 'Name' field as Lookup field and sorted the Lookup field value using 'Last name' . Follow the steps below to sort a Lookup field using Deluge script.

1.1 Go to 'Edit Application' --->Tap on 'Workflow'

1.2 Tap on 'New Workflow' button

1.3 Choose the form on which you want to run the Workflow and choose 'Created or Edited'

1.4 Tap on 'Add New Action'

1.5 Select 'Deluge Script'

1.6 Select 'On load'

1.7 Paste the copied code here from code snippet given below and tap on the button Save then open the form