#!/bin/bash
s='"ID","Name","DOB","Age","Address","City","State","Country","Phone number"
"123","ABC","12/20/2020","0","No.38,3rd st, RRR NNN, TRT",,,,"9999999999"'
perl -pe 's/"([^"]*)"|,/defined($1) ? $1 : "|"/ge' <<< "$s"
IyEvYmluL2Jhc2gKcz0nIklEIiwiTmFtZSIsIkRPQiIsIkFnZSIsIkFkZHJlc3MiLCJDaXR5IiwiU3RhdGUiLCJDb3VudHJ5IiwiUGhvbmUgbnVtYmVyIgoiMTIzIiwiQUJDIiwiMTIvMjAvMjAyMCIsIjAiLCJOby4zOCwzcmQgc3QsIFJSUiBOTk4sIFRSVCIsLCwsIjk5OTk5OTk5OTkiJwpwZXJsIC1wZSAncy8iKFteIl0qKSJ8LC9kZWZpbmVkKCQxKSA/ICQxIDogInwiL2dlJyA8PDwgIiRzIg==