The first step is to download all your transactions from fex and upload it into Koinly. There are a couple of ways you can do that:
If you decide to import CSV files, you have to 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 appear as Income on your final cryptocurrency tax reports!