Well, many of us have sought out similar information, probably with mixed results.

2008 Volvo XC90 Owners Manual:
Go to section 02 Instruments and Control, then to paragraphs 54-55. As would be expected, the manual doesn't instruct the owner how to reset; i.e., can only be "reset by a trained and qualified Volvo service technician." I think most owners manuals will say the same thing.

That said, there are lots of sites on the web (You Tube, blogs etc.) that give advice on resetting Volvo service reminders, but many of them are specific to certain years and models only. (My daughter successfully found instructions for her 2010 S40).

ipd is usually a credible source; here's what it says: https://www.ipdusa.com/blogs/103/howto-reset-service-reminder-indicator-on-1998-2009-volvos

These ipd instructions work for our 2000 V70. But I cannot attest on whether it works for a 2008 Volvo model.