SharePoint Employee list that for each employee item contains a Supervisor Column that is a People Data type.  Supervisors change.  Looking to mass update workflow (SharePoint On-Prem) the Employee List when a New Supervisor is added to Supervisor List:

input the old " Former] Supervisor" and new " New] Supervisor" into the New Supervisor List, then upon submit, which triggers a workflow to search in Employee List "Supervisor" = "old value" then update it with the "new value".

So, in this Case…  old “ Former] Supervisor” = Shultz, Marie and want to replace all instances of Shultz, Marie in Supervisor column with Williams, Christine (aka “tNew] Supervisor”).

I have tried to keep it simple with no luck: 

Any suggestions would be very helpful.