how do i do this?

What you want is very close to:
https://www.experts-exchange.com/questions/20932619/Search-Replace.html

Download from:        http://www.geocities.com/esoftbg/ee/Q_20932619.zip working example of above question

an older sample
which can use multiple filemasks

unit filesearch_with_masks_u;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TForm1 = class(TForm)
    Memo1: TMemo;
    ListBox1: TListBox;
    Button1: TButton;
    CheckBox1: TCheckBox;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

uses filectrl; //just for selectdirectory

procedure FindFile(APath : string;
                  IncludeSubDirs : Boolean;
                  FileMasks : TStrings;
                  ResultList : Tstrings
                  );
var
  srec : TSearchRec;
  Path, FileName : String;
  i : integer;
begin
  path := APath;
  if path[length(path)] <> '\' then
    path := path + '\';

  if not assigned(FileMasks) then
    raise exception.Create('No Masks given');
  if not assigned(ResultList) then
    raise exception.Create('No ResultContainer given');
  for i := 0 to filemasks.Count - 1 do
  begin
  // CurrentDirectory
    if findfirst(Path+filemasks[i],faanyfile,srec) = 0 then
    begin
    repeat
      If Not(srec.attr and fadirectory > 0) then
      begin
        ResultList.Add(Path+SRec.Name)
      end;
    Until findnext(srec) <> 0;
    end;
    FindClose(SRec);
    { SubDirectories }
    If IncludeSubDirs then
    begin
    if FindFirst(Path+'*.*',FaAnyFile,Srec) = 0 then
    begin
      repeat
        // StartRecursion
        if not(Srec.Name[1] = '.') and (srec.attr and fadirectory > 0)then
          FindFile(Path + Srec.Name + '\' + FileName,IncludeSubDirs,FileMasks,ResultList)
      Until findnext(srec) <> 0;
    end;
    FindClose(SRec);
    end;
  end;
end;


//usage sample
procedure TForm1.Button1Click(Sender: TObject);
var path : String;
begin
  if selectDirectory('Select Directory','',path) then
  begin
    listbox1.Items.Clear;
    findfile(path,checkbox1.Checked,memo1.lines,listbox1.items);
    showmessage(inttostr(listbox1.Items.Count)+' files found');
  end;
end;

end.

meikl ;-)