Nintex form populate default choice value based on list look up field

The following are the form fields belonging to a SharePoint 2016 Document Library:

1. Content type: List Look up values as follows:

1. Thesis (default to B1)
2. Reports
3. Etc
   
   B. Choice field not connected:
   1. 1|I want to share
   2. 2|I do not want to share
      
      C.Hide “Approver” field if B=2, or Hide “Reason for not sharing” field if B=1

My users will select the Content type e.g. A1-Thesis and the form should show B1 I want to share as the default and system still allow the user to select B2 if he does not want to share.

How can the above be implemented?