The first and usually the only step is to download all your transaction data from Coss wallet and upload them to Koinly. There are a couple of ways you can do that:
If you want to import CSV files, you must make sure to import your deposits/withdrawals and trades for ALL previous years and not just the current one!
That's all you have to do. The only other thing to keep in mind is to tag your airdrops/forks so they show up as Income on your generated cryptocurrency tax documents!