Adjusting loco lights

Please excuse my stupidity, if I have missed something obvious.  I have bought a couple of Bachmann Class 37s and found two of these 36-557, 21 pin, 1 amp, 4 function decoders in my spares box.  They fit and run okay, but can I figure out how to dim the head an tail lights, can I hell.  The online instructions are of no use either. The older 36-554, 3 function decoders were simple, just adjust CV 63.  But this one's a nightmare.  I'm sure I'm not the first to encounter this problem.  Any help is much appreciated, I cant afford to lose any more hair!  Regards Charlie

Bachmann 36-557 21-pin Decoder - DCC Discussion Topics (not questions) - RMweb

has about changes to the decoder