How to Set the look up value by default?

 function loopupvalue()
    {  var lookupValue = new Array();
        lookupValue[0] = new Object();
        lookupValue[0].id = "475B158C-541C-E511-80D3-3863BB347BA8"; //Guid of the A. Datum//
        lookupValue[0].name = "A. Datum";
        lookupValue[0].entityType = "account";
        Xrm.Page.getAttribute("parentcustomerid").setValue(lookupValue);
           
   }