how to get yahoo off my browser

Open Safari’s preferences and remove or disable any extensions you don’t recognize. If it persists, click here and run the tool.

The basic steps are:

1. Click the Tools icon at the far right of the browser window.
2. Select Internet options.
3. In the General tab, find the Search section and click Settings.
4. Select Google.

You have adware/malware installed. Use  Malwarebytes Anti-Malware for Mac. It may be necessary to run more than one scan. After scanning a couple of times, restart the computer and test. If necessary, follow the manual instructions.  Do not download any other programs that are listed in the articles.   Malwarebytes uninstall

See if the below helps. I would scroll down to the below or you might fall asleep.

Step 1. Eliminate Yahoo Redirect from Windows

Step 2. Delete Yahoo Redirect from Mac OS X

Step 3. Uninstall Yahoo Redirect from Internet Explorer

Step 4. Remove Yahoo Redirect from Microsoft Edge

Step 5. Erase Yahoo Redirect from Mozilla Firefox

Step 6. Get rid of Yahoo Redirect from Google Chrome

Step 7. Eliminate Yahoo Redirect from Safari

https://www.2-spyware.com/remove-yahoo-redirect-virus.html

Go to Safari Preferences/Extensions, uninstall any you don't recognize, and then turn all extensions off. Test. If okay, turn the extensions on one by one until you figure out what extension is causing the problem.