Use the below code.
You need to register this method on load. You also need to replace the field schema values.
=============
function loadParentDetailsToChild() {
try {
var parentAccountId = parent.top.opener.Xrm.Page.data.entity.getId();
var parentAccountName = parent.top.opener.Xrm.Page.getAttribute("name").getValue();
var parentAccountLookup = new Array();
parentAccountLookup[0] = new Object();
parentAccountLookup[0].id = parentAccountId;
parentAccountLookup[0].name = parentAccountName;
parentAccountLookup[0].entityType = "account";
Xrm.Page.getAttribute("parentcustomerid").setValue(parentAccountLookup);
}
catch (err) {
console.log(err.message);
}
}
==========================
Hope this helps.
