ensureIndexTemplate and indexTemplate not working

I want to add **mappings** to the index using **indexTemplate** . 
i set **ensureIndexTemplate** to **true** and i put `indexTemplate: {
      mappings: {
        properties: {
          co: {
            index: true,
            type: "keyword",
          },
          age: {
            type: "integer",
          },
        },
      },
    }`
    but nothing happened. 