Hello I wish you at the same time 
for help that I have avast premium security in my pc and I have windows 10 64-bit and when I go to do it via avast via restart check it will find an error but you will not find the virus and when I did a NEW installation of windows 10 64-bit and avast will still find it for me and I did it 3 times and stqale will find it for me and now I don’t know where I’m making a mistake please thank you for your help 8).
@Koma.1
You have posted in the Avast Beta testing section of the forum.
If you are not testing a Beta version of Avast then you would be better posting in the main AV section here:
https://forum.avast.com/index.php?board=2.0
From your post, see you have Win10 and Avast Premium. Is it a “Boot Scan” you are finding an error? If so what is the error message?
A screenshot of the error message would be good to aid understanding of your issue. Use the “Attachments and other options” link when posting.
I’m sending it here