What can I use to replace symantec?

Nothing. It was never needed nor is any similar app.. Macs have built in protection.

Should you still desire something...

There is a free Malwarebytes which may take care of it...

https://www.malwarebytes.com/mac/

See also here:

Effective defenses against malware and ot… - Apple Community

Agree with @ BobTheFisherman on this one.

The Mac doesn't need or benefit from third-party antivirus, cleanup or speedup apps. They often cause more trouble than they claim to prevent.

Some light reading:

Protecting against malware in macOS - Apple Support

XProtect Explained: How Your Mac'S Built-in Anti-malware Software Works - howtogeek.com