The first - and in most cases, the only - step is to download all your data from BITBOX and import them into Koinly. There are a few ways you can do that:
Note that if you want to import CSV files, you have to make sure to import your deposits/withdrawals and trades for ALL years !
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!