Missing original FIAT -> bitcoin. Tax issues

Describe the problem:
I’m trying to generate multiple tax reports for my bitcoin gains. However, the exchange I originally purchases bitcoins from is long gone and I do not have any records from that. Can I somehow treat all bitcoins deposits as “purchases” (with value 0). That way I will tax for the full sell amount, but I assume this is the only way. Does Koinly support this?

Which exchange/wallet is this regarding?
Kraken

How did you import data into this wallet?
CSV

What have you tried to fix this so far?
Have looked into settings, but not sure if an option for this exists.

I had the exact same issue, what you do is make an ‘xyz’ wallet, and then set all the deposits as transfers from the ‘xyz’ wallet and then it will set the deposits as zero cost basis.