I used PUT MAPPING API to update my fields in existing ES. Will i need to reindex the new fields? What should i do to reindex the docs ? Also what is the format of the json to be used in put mapping?

Elastic Stack Elasticsearch
1

{
"dynamic":"strict",
"_all":{
"enabled":false
},
"properties":{
"CountryName":{
"type":"string",
"analyzer":"case_insensitive_analyzer"
}
}}