you can remove the first characters with a number of functions, e.g.
$regexp(%fieldname%,'^...(.*)',$1)
but as you do not have a common pattern
(sometimes just 3 characters, sometimes 5 like in "B2_-_Tom Hades - Connect") you will be left with some remainders.
Why don't you import the data into tag fields first so that the amorphous string become more structured data and then write a new filename with data from the tag fields?