ModifyShare.cs

/// <summary>
/// Modifies the access to a shared record.
/// </summary>
/// <param name="service">Authenticated client implementing the IOrganizationService interface</param>
/// <param name="principal">The user, team, or organization to modify rights to the shared.</param>
/// <param name="access">The access rights to modify</param>
/// <param name="record">The shared record</param>
static void ModifyShare(
   IOrganizationService service,
   EntityReference principal,
   AccessRights access,
   EntityReference record)
{
   PrincipalAccess principalAccess = new()
   {
         AccessMask = access,
         Principal = principal
   };

   ModifyAccessRequest request = new()
   {

         PrincipalAccess = principalAccess,
         Target = record
   };

   service.Execute(request);
}