how to clear malware on a Mac book

What malware, you do not say...(?)

To trouble shoot further you can:

—A SafeBoot Start up your Mac in safe mode - Apple Support will sort many anomalies

Does a quick disk repair before it fully boots up, and certain system caches get cleared and rebuilt, third party system modifications and system accelerations are disabled temporarily.

Login and test. Reboot as normal and test. Caches get rebuilt automatically.

This test will tell you if third party interference; most extensions etc are not loaded in safe boot mode.

—Test issue in another user (or guest user) account Change Users & Groups settings on Mac - Apple Support

This will tell you if it a universal issue or isolated to your user/admin account. 

***if you have a wireless keyboard with rechargeable batteries connect the charging cable before booting to Safe Mode. 

This will make it act as a wired keyboard and a successful Safe Boot mode.

unplug all non-essential peripherals when testing

Uninstall all third party apps that are Cleaners/Optimizers/VPN/Anti-Virus

all known to cause issues on the macOS

Adding to what Leroy said, if your Mac will stay on long enough, you can download Malwarebytes:

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

and have it check your system. If that doesn't turn up anything, or you can't get it to run, you can see if Apple's diagnostics turn up any issues:

Use Apple Diagnostics to test your Mac - Apple Support

If you can't even get the diagnostics to run, I'd recommend taking the Mac to an Apple Store or authorized Apple service center for evaluation.

If diagnostics runs but doesn't report any issues, post back and we can go from there>

Regards.

In addition to the great guidance provided above by user @leroydouglas, there are two popular utiliities they we user here in the Community for troubleshooting issues such as yours.

One is the Malwarebytes utility application.  The app was designed solely to seek out adware and known malware and remove it. It’s a popular tool among veteran users here in the Community. Run the app and see if it can identify any malware you may have accidentally installed. The free version is probably all you need at this point to identify and quarantine potential problems.  Remove what is found from the quarantine.

The other is EtreCheck (free). Please run an EtreCheck evaluation of your Mac and post the generated report back here in a reply. EtreCheck is a safe and highly regarded utility from a trusted developer and respected ASC contributor. The diagnostic report will not include any personal info. It simply gathers specifics about hardware performance and installed software that might be in conflict with the OS.

Please navigate to EtreCheck.com to download utility. Be sure to Allow Full Disk Access when you install the app. Once you’ve run the app and created your report please post it with your reply to this message. 

Please note you must upload the full report. To see how, please click >  How to use Add Text when posting… EtreCheck Report.

We’ll use your EtreCheck report to look for the things that may be causing your problem and advise how to correct them.