Most findings about fitting are in this thread.
You will find a couple of hexagon Allen keys in with the bulbs, these fit the grub screws on the bulbs. One grub screw is holding the body of the bulb static in relation to the orientation tabs on the bulb mounting flange - there are instructions with the bulb which number to line up for RH drive car, the people on here who have bought the bulbs have found they are already set up properly for UK. Just make sure the grub screw is nipped up properly. The other grub screw locks the heatsink to the rear of bulb, the heatsink screws on and make sure grub screw is fully slackened off before trying to unscrew it. The Allen keys are very close is size so check you have the correct one. You will have to screw heatsink off to fit bulb, with the heatsink off you can easily flick the spring clips on the back of Honda reflector that hold bulb in place ( it makes bulb easier to fit if you bear in mind that the widest of the 3 tabs on the bulb flange faces vertically upwards to line up with its slot in reflector flange ) once bulb is clipped in you can refit the rubber seal that you removed when you took old filament bulb out - then rescrew the heatsink back onto bulb, heatsink can screw on two ways, make sure the threaded portion of heatsink that sticks out screws on first so that main finned body of heatsink sits away from back of bulb and more towards bulkhead, this improves the air flow around heatsink by taking fins further away from rubber grommet. Hand tighten heatsink and do not worry about tightening the grub screw as you will find it impossible to do it anyway, mine have been in over two years with no grub screw fitted, let alone tightened. I did smear a bit of computer heatsink compound on my threads, but it gets really messy. They supply cable ties with bulbs to fix the bulb power supply ( constant current driver ) to somewhere convenient nearby. I found the heatsink never really gets hotter than 40 to 50 degree C ( can easily hold you hand on it) so it is quite safe to mount near cables, the power supply module barely gets warm.