Hello 
I have a question for you!
When a virus is in the Chest/quarantine, what should I do? Should I delete it or Avast will do it automatically?
So what does a virus do in the chest??
You have done the right thing, ‘first do no harm’ don’t delete, send virus to the chest and investigate.
There is no rush to delete anything from the chest, a protected area where it can do no harm. Anything that you send to the chest you should leave there for a few weeks. If after that time you have suffered no adverse effects from moving these to the chest, scan them again (inside the chest) and if they are still detected as viruses, delete them.