Boot-scan help needed, please

I am a new user of the free version of Avast. When I ran Avast it found a Trojan and advised me to move it to the chest and then schedule a boot-scan.

I read the Help screens and there is a warning that moving or deleting system files is dangerous. Well, when I went to schedule a boot-time scan there are no options for dealing with system files differently than than what is in the default options. The Advanced options section for dealing with system files is greyed out and cannot be accessed.

I do not want to mess up my system, but a boot-time scan is apparently needed. What should I do?

What part exactly is grayed?
If you have the “action” set to “Ask for action”, then yes, the bottom combobox is disabled… but avast! will ask you for every detected file what to do about it.