How to add a checkbox in InstallDir Dialog?

I found some articles which says that we need to add WixUI_InstallDir.wxs and InstallDirDlg.wxs files to our WiX source code and have to edit them to add a checkbox. But, I don't find InstallDirDlg.wxs to edit and incude it in my wix source code. I am using WiX 3.11.1 version and please let me know the best way to add a checkbox.