How do you reset the "Check Engine Lights"?
 

I know very little about cars.

I have a 2009 Audi A8 with 15,000 miles. It has been regularly maintained at the Audi dealership for all these years.

A very night, driving home from work, the "Check Engine Light" came on and remained . i have no idea, so search on the net. someone told me use ELM327

i have bought an MINI ELM327 here, follow the user manual it can read the error code but it seems do nothing to reset the CET. it is very cheap so I do not think it will solve my problem well.
if someone has has a cheap, easy, free method, pls help me:)
if it is necessary for me to invest in some diagnostic tools to aid in the troubleshooting of my Audi A8, can you recommend me an useful one?
some friends told me Autle MaxiDAS DS708. is it a good one?:confused:

Ignore my bad English