Yahoo search keeps taking over Chrome

If it keeps coming back after you change it, something is forcing it. Go to Settings > Search engine > Manage search engines, set Google as default and delete the Yahoo entry, then go through your extensions and remove anything you don't recognise, the search hijackers often disguise themselves as PDF converters or weather tools. If the three dot menu shows Managed by your organization on a home PC, a policy has been installed. Type chrome://policy in the address bar to see it, and run a proper malware scan, because that one won't go away just by changing settings.