maybe you need to show hidden files on your system, too see all the files in the trainer-install-folder

then open the files "MT-X Installation\Medieval 2 Kingdoms\Medieval2Kingdoms.txt" and copy the last line to a new one at the end - so the file should look like this
you need to replace the red string with the exact modname, which you probably can see, when viewing the properties of the shortcut for this mod
after saving the file (on Vista/Win7 you may need to open the file with an editor with admin-rights), you can select the ThirdAge entry in the trainer, when selecting "Medieval 2 Kingdoms" as game and view the versions