This is a common issue - Yahoo search hijacking your browser is usually caused by an unwanted browser extension or potentially unwanted program (PUP). Here's how to fix it:
1. Check your browser extensions - Go to your browser's extensions/add-ons page and remove any suspicious or unfamiliar extensions, especially ones related to search or toolbars.
2. Reset your search engine settings - In your browser settings, manually set your preferred search engine back to Google (or whatever you prefer).
3. Check your installed programs - Go to Windows Settings > Apps and look for any recently installed programs you don't recognize, especially ones with names like "Search Manager" or similar.
4. Run a malware scan using Windows Defender or a trusted anti-malware tool like Malwarebytes to make sure there's nothing else lingering on your system.
Let me know if you need specific steps for your browser!