Normally you delete them. If you got a virus infection, you don’t want to keep walking around with it, you want it to be gone.
When Avast detects one, also enable “if needed remove at next boot”
I (we) may be able to give more specific help if you tell us more, like the name of the virus(es), what location the infected files are in, what version of avast etc etc. In the mean time I suggest you click the link in my signature and follow the steps on that page to clean and protect your system