Create and search nested document

[Odunayo_Ogundepo]

Hi,

I have a document that looks like this

{"rid" : "1", 
  "oid":"23,  
  "data" :{
         "ticks": [{
              "a": "xx",
               "b" : "yy"
                 },
              {
              "a": "xxx",
               "b" : "yyy"}
]}

I see that Elasticsearch 7.14 does not allow explicit definitions of mapping when creating indices. how can I index this such that I can search "b" field and return only this source of documents that match the query {
"a": "xx",
"b" : "yy"
}