oh boy, I thought all companies out thre make their fixtures at least with dimming knod. If you don't have a dimming knod for the fixture, then nothin really you can do to dim the light. As dimming the fixture require lower the current going thru the LED
Without dimming, you need to be very careful especially if you already have coral in there, you are gambling with the coral. You might be lucky that all of them are fine no problem. Or you will find some coral would start melting or bleaching.
If your fixtures comes with 2 power cord, 1 for white 1 for blue, I would suggest to just keep the blue on only for now, and maybe turn on the white LED
after at least a week.