Since ptracker 3.2.x there is an installer to easily install ptracker. Just execute the installer, and make sure the correct AC installation dir is selected in the installer window.
Apps must be enabled after installing in the AC launcher under Options->General->UI Modules. Just check the ptracker app and afterwards you'll find the "PT" icon in the game's side bar.
C:\Program Files (x86)\Steam\SteamApps\common\assettocorsa\apps\python\ptrackerand install ptracker again.
<my documents>/plugins/ptracker. Note that this will delete your local lap database.