Blockchain – What should I do if I purchased Bitcoin in 2009 or 2008?

I would like to find the Bitcoin I purchased by paying 100,000 won in the past.

At that time, I remember making purchases through bank transfer or small payments over the phone. Is it right to purchase this way? I think I formatted Windows on that disk and installed it about 4 or 5 times. Is recovery possible? (Currently, the wallet.dat file cannot be found.) I connected the drive to another desktop, installed Bitcoin QT, and synced over three days. Currently, the blk files of newly installed qt are checked from blk04197 to blk04209. blk files start from blk00000.dat. Why was it made like this? If it’s strange, is it correct that there should be files from blk00000.dat to blk04196.dat? If so, can you find that file? Thanks for your answer. I am a person who doesn’t know much about computers.