Search yahoo search engine

1. On the top menu select Safari => Preferences.
2. Select Extensions tab.
3. Select an extension you want to delete and click Uninstall button next to it.
4. Go to General tab.
5. Select what you want Safari to open on start-up, new windows, new tabs and homepage.
6. Go to Search tab.
7. Select the search engine you want.

If that doesn't work...

Post a report from this please...

EtreCheck is a simple little app to display the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to help people help you with your Mac.

http://www.etresoft.com/etrecheck

There is also Malwarebytes…

https://www.malwarebytes.com/mac/

You can try run the one time https://www.malwarebytes.com/mac/

to remove adware, malware, hijack your search engine ware