I want Google as my search engine, not Yahoo

On the Chrome app for Mac, try the following steps:

1. Open Google Chrome.
2. At the top right, click the vertical three dots next to your profile picture
3. click on Settings.
4. select search engine from the panel on the left hand side of the settings page
5. choose the search engine you prefer (Google in this case)

If the above steps do not work, I suggest deleting and reinstalling Google Chrome.

To delete an app from your Mac:

1. Locate the app in the Finder. Most apps are in your Applications folder, which you can open by clicking Applications in the sidebar of any Finder window. Or use Spotlight to find the app, then press and hold the Command (⌘) key while double-clicking the app in Spotlight.
2. select the app and choose File > Move to Trash or drag the app to the Trash

After deleting Google Chrome, reinstall the application here (https://www.google.com/chrome/)

If you suspect that there is malware on your device, I recommend scanning your Mac with Malwarebytes. I use the free version and it helps remove any suspicious content from my Mac. You can download it here https://www.malwarebytes.com/mac/

Let me know if these steps helped and if they solved your issue