JAVASCRIPT

set value lookup javascript dynamics 365

var lookupValue = new Array();
lookupValue[0] = new Object();
lookupValue[0].id = "{727504ed-64c5-4bc8-ac22-0a3071c427e3}"; // GUID of the lookup id
lookupValue[0].name = "Goutam Das"; // Name of the lookup
lookupValue[0].entityType = "contact"; //Entity Type of the lookup entity
Xrm.Page.getAttribute("FieldName").setValue(lookupValue); // You need to replace the lookup field Name..