Not sure if I totally understood what you need. And, I'm sure there are better ways to do this... But:
This setup assumes that there are patterns in vendor column. It uses wildcards "*"&A1&"*" and if statements to compare the items.
VLOOKUP also allows wildcards, and it would be good to use that because it looks in a
range of cells rather than looking in each cell individually (as I have done). I couldn't figure out how to set it up with vlookup for this though... My technique of looking for a pattern cell-by-cell will be okay until you have more than a dozen or so patterns. Then the formula will get a bit cumbersome.
Note also that I have the exported-from-your-bank data in one tab, then the other tab reads from that tab. This prevents you from having to re-enter the 'account' column each time.
Like I said, there are probably better ways to do this!