Get PartyList lookup field in Email/Activities entity update partyid record

Get the partylist lookup value and check the lookup value is contact and update the contact  

Entity fromActivityParty = targetEntity.GetAttributeValue<EntityCollection>("from").Entities

                .Where(x => x.GetAttributeValue<EntityReference>("partyid")?.LogicalName == "contact")

                .FirstOrDefault();

         if (fromActivityParty == null) return;

         EntityReference contactReference = fromActivityParty.GetAttributeValue<EntityReference>("partyid");

Entity contact = new Entity("contact", contactReference.Id);

contact["fullname"]= "ApyCRM";

service.Update(contact);