Edit line in a file . class and recompile

Question

I have a file called WEB.class that I imported from a.WAR file where I have the strings to connect to our database with the following code:

@Produces({"application/json"})
   @GET
   @Path("/ZoomNotasFiscais")
   public Response ZoomNotasFiscais(@QueryParam("empresa") String empresa, @QueryParam("codCliente") String codCliente, @QueryParam("loja") String loja, @QueryParam("search")) {
     try {
       sql = new SQL("cliente");
       Parametros parametros = new Parametros();
       try {
         String query = "SELECT D2_DOC AS [NF], SUM(SD2.D2_TOTAL + SD2.D2_VALIPI + SD2.D2_DESCON ) AS [VALOR] FROM " + 

The only thing I need to do is add a new field to the database query within the query string. Example:

String query = "SELECT NOVO_CAMPO AS [NOVOCAMPO], D2_DOC AS [NF], SUM(SD2.D2_TOTAL + SD2.D2_VALIPI + SD2.D2_DESCON ) AS [VALOR] FROM " + 

The only doubt I have is how to change this line of the WEB.class file and save again as WEB.class

I already downloaded the decompilers and managed to see the code, but none of it has the option to edit the code and save this file again . CLASS

How to change only this line and add the . class again in the project? I need to create a new. java file?