The sidelights (or parking lights) are regular incandescent bulbs which look very yellow next to the HID main lights.
The good news is that replacement LED bulbs are easy to source and fit. I have been using these bulbs in my cars for years now and they have never let me down: Autobulbs Direct
Reaching in you’ll be able to unclip the wire connector. The bulb holder then twists to release. Withdraw the holder and swap the bulbs over. If the bulb doesn’t work first time around then you have probably fitted it the wrong way – they only work one way round, just turn it over.