The first and usually only step is to download all your transactions from Coincheck and import it to Koinly. There are a couple of ways you can do this:
Note that if you decide to import CSV files, you need to make sure to import your deposits/withdrawals and trades for ALL years !
That's all you have to do. The only other thing to be vary of is to tag your airdrops/forks so they show up as Income on your generated cryptocurrency tax documents!