How can i fix this error Mapper for [description] conflicts with existing mapper:Cannot update parameter [analyzer] from [my_analyzer] to [default]

am new to elastic search.please help me out with this problem.

Am using elastic search version 7.13.2 .

I created an index with a custom analyzer and filter like this

PUT /analyzers_test
{
  "settings": {
    "analysis": {
      "analyzer": {
        "english_stop":{
          "type":"standard",
          "stopwords":"_english_"
        },
        "my_analyzer":{
          "type":"custom",
          "tokenizer":"standard",
          "char_filter":["html_strip"
            ],
            "filter":[
              "lowercase",
              "trim",
              "my_stemmer"]
        }
      },
      "filter": {
        "my_stemmer":{
          "type":"stemmer",
          "name":"english"
        }
      }
    }
  }
}

Then i created a mapping for the document i will have and specified my custom analyzer i created earlier (there is no document in the index yet) like so:

PUT /analyzers_test/_mapping
{
    "properties": {
      "description":{
        "type": "text",
        "analyzer": "my_analyzer"
      },
      "teaser":{
        "type": "text"
      
      }
    }
}

When i try try to create a document like so

POST /analyzers_test/1
{
  "description":"drinking",
  "teaser":"drinking"
}

i get the following error

{
  "error" : {
    "root_cause" : [
      {
        "type" : "illegal_argument_exception",
        "reason" : "Mapper for [description] conflicts with existing mapper:\n\tCannot update parameter [analyzer] from [my_analyzer] to [default]"
      }
    ],
    "type" : "illegal_argument_exception",
    "reason" : "Mapper for [description] conflicts with existing mapper:\n\tCannot update parameter [analyzer] from [my_analyzer] to [default]"
  },
  "status" : 400
}