how to clean the viruse in my imac

First, there is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus, VPN or security apps on your Mac.  This user tip describes what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community.  

There are no known viruses, i.e. self propagating, for Macs.  There are, however, adware and malware which require the user to install although unwittingly most of the time thru sneaky links, etc.   

Anti Virus developers try to group all types as viruses into their ad campaigns of fear.  They do a poor job of the detecting and isolating the adware and malware.  Since there are no viruses these apps use up a lot of system resources searching for what is non-existent and adversely affect system and app performance.

There is one app, Malwarebytes, which was developed by a long time contributor to these forums and a highly respected member of the computer security community, that is desshoigned solely to seek out adware and known malware and remove it.  The free version is more than adequate for most users.  

Also, unless you're using a true VPN tunnel, such as between you and your employer's or bank's servers, they are useless from a privacy standpoint: Public VPN's are anything but private.  

That being said what makes you think you have a virus?

There are no viruses in the wild for Mac OS. Perhaps if you told us why you think you have a virus we can help you out. You may have installed other malware or downloaded some adware which can cause unusual behavior and if that is the case, download the free version of Malwarebytes.com and run it.

Whatever you do, DO NOT install any third party antivirus, cleaning or any other "maintenance" apps or you stand an excellent chance of making a mess of Mac OS.

See also:

Effective defenses against malware and ot… - Apple Community