Well based on the randomly named folder and the randomly named file name (zero hits on the file name on google, other than this topic), so first the detection appears to be good.
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, avastUI, Maintenance, Virus Chest) and if they are still detected as viruses, delete them.
So when it comes time to delete, having opened the chest right click on the file you want to delete on the pop-up (see image, is this what you see ? ) select yes and it should be deleted.
So I don't see any Apply, so my guess is that you are trying to delete this from the old report/log of your scan and that won't work as it is historic, you have already taken action on that detection by moving it to the chest. So it won't exist in the original location, it is in the chest so it needs to be deleted 'from within the chest' as outlined above.