Go to either:
C:\Program Files\Steam\steamapps\common\railworks or
C:\Program Files\Steam\steamapps\common\railworks\Assets
In one of them you are likely to find an Ovvee flder (I don't have any Ovvee add-ons installed at present so cannot be certain exactly where it will be)
They are usually named fairly sensibly and a lot of the other other traction I have installed has a PDF manual in the relevant folder.
There are probably other ways to get to it but I know this one is likely to work
EDIT: This assumes Steam etc is installed to the default location and to C: