The first - and in most cases, the only - step is to download all your transaction data from bitcoin.de and upload it into Koinly. There are a couple of ways you can do this:
If you decide to use CSV files, you need to make sure to import your deposits/withdrawals and trades for ALL previous years and not just the current one!
That's pretty much it. Don't forget to tag your airdrops/forks so they show up as Income on your generated crypto tax documents!