Update :
Current bitbucket-pipelines.yml config :

• curl -s -S -L -O https://$ {BB_AUTH_STRING}@api.bitbucket.org/2.0/repositories/lorainelab/iipc/src/master/2020-03-25-developerID_application_igb.p12
  
  Where 'iipc' is a forked repo of 'IGB Installer Private Content' and which does not contain the new mac certificate.
  (Note : The curl command creates a new file even if the file doesn't exist in the repo, so we never got any error like 'file does not exist error')
  
  Prof. [~aloraine] We need to change in the bitbucket-pipelines.yml config file :
  iipc to igb-installer-private-content as following or add new macOs cert file in the iipc repository
  - curl -s -S -L -O https://${BB_AUTH_STRING}

  @api.bitbucket.org/2.0/repositories/lorainelab/igb-installer-private-content/src/master/2020-03-25-developerID_application_igb.p12

Fork is now up-to-date.
cc: Pooja Nikhare Prutha Kulkarni

Release installer built on team repository following update of fork.
cc: Pooja Nikhare and Prutha Kulkarni

[~aloraine] Pooja Nikhare
I am able to install the recently built installer on the mac now.

Marking this issue as done.
Thank you Pooja Nikhare and Prutha Kulkarni for your step-by-step notes.
What you have written above will help greatly with future efforts.