Can you paste that output here? If you click on the </> icon it will give you some space to put it so the formatting is correct. We can then have a play and see what we can do.
[
{
"JSON_F52E2B61-18A1-11d1-B105-00805F49916B": "{"customer":[{"FullyQualifiedName":"ABC Company Limited","PrimaryPhone":{"FreeFormNumber":"+88 8888 8888"},"BillAddr":{"Line1":"Address Line 1","Line2":"Address Line 2","Suburb":"Suburb","City":"City","PostCode":"8888"}}]}"
}
]
It isn’t pretty but here is one option you could use, The first node mocks the output you get from SQL then with a set node I convert the straing to a json object with JSON.parse() then in the ItemList node I just extract the part you want using the output variable from the set node along with customer.
There is going to be a few ways to do this but this is the first and quickest I thought of