Query Optimization: Getting Customer IDs without JOIN and Handling UNNEST

SQL++
,
3

This is from 1 document called Route
SELECT A.RteId,B.LocNm
FROM Test A
UNNEST SrvLoc B
WHERE A.$Type = “Route” and B.LocTyp=“DC”
and A.RteId IN

and this is from second documnet called customer
SELECT RAW b.RteID
FROM Test a
UNNEST CustRel b
WHERE a.$Type = “Customer”
and a.custid IN [“2003”,“2004”]
and b.cd=“01”

now if i do A.Rteid IN ( SELECT FROM CUSTOMER DOCUMENT)

I get RteId and LocNm from the above … How can i get customerid as well here .