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