when would the camshaft belt on a Mercedes Benz 350 cls have to be changed. on 2006 Mercedes-Benz CLS500

And if I did the service myself how would i reset the computer

Asked by for the 2006 Mercedes-Benz CLS500
ok it has a timing chain not a belt. is it making noise? this is a huge job for a good tech.DO NOT ATTEMPT THIS YOURSELF