Getting off the internet is just an additional precaution and as long as you don’t do any actually browsing,
you can bypass that step.
Avast asks for permission to boot into Safe Mode so it can perform the removal of items that can’t be deleted
using the normal uninstall process via Programs and Features. Just grant it permission and it will reboot to safemode and do it’s job.
Once done reboot and you’ll go back to regular mode at which time you can install Avast again.
You can watch the following video I created last year to guide you through the process.
https://youtu.be/p-h3myRD51A
