If you still need help, please can you be more specific about the nature of your problem?
Chrome is a web browser and not a search engine, whereas Yahoo is (among other things) a search engine and not a browser. So you can't 'go from one to the other'.
Please tell us which browser you're using. (i.e. assume it's Chrome but it would help to be sure). Then explain exactly what it is that's changed for you. (i.e. has your browser's home page changed or has the default search engine it uses changed?)