Although there are other approaches you may take, I'm assuming the "export to excel" function is part of a front-end package like DataTables.
If so, you must intercept the data prior to the export operation. From the DataTables, this.
Example:
var export_data = table.buttons.exportData({
    format: {
      body: removeRupee
    }
  }); 
function removeRupee(data, columnIndex){   
  return ((columnIndex === 2 || columnIndex ===4) ? data.slice(0, -1) : data)   
}
If the export is generated from the backend, then I suggest you don't keep the currency in the same column as the value.