Safari is now part of the OS, so the only way to reinstall Safari is to reinstall the OS.
Safari – Popup takes over
Safari – Popup takes over (2)
Popup remover – Scam Zapper
If the pop-up reloads, force quit Safari (command - option/alt - esc) and reopen with the shift key held down. If that doesn't work, disconnect from the Internet, go to Safari/History and delete the website. Quit and reopen with the shift key held down. Then reconnect to the Internet.
Safari -Tech support scam pop-ups
You may have adware/malware installed. Try downloading this program which was written by Thomas R, a long time poster. The program will search for malware/adware The program will do the work for you which makes it easy. It may be necessary to run more than one scan. After running the scans, restart the computer.
Malwarebytes Anti-Malware for Mac 10.10 and later
Malwarebytes uninstall