The functions.php file in Thesis 2 is actually named custom.php
It is located in (wp-content/thesis/skins/your_skin_name/custom.php). All files that are relative to your currently active skin are located in that same folder.
Although I now see you are using Crayon which is a much easier option.
Files stored in (wp-content/themes/thesis/…) are the core Thesis files and should not be edited. If you can remember what you altered there it might be advisable to change it back to how it was before, although those files may get overwritten at the next Thesis update.
Another way to undo any changes to the core files would be to FTP in to your server and overwrite any files you have changed in (wp-content/themes/thesis/) from a downloaded copy of the relevant version of Thesis to the one you are currently using.