The first and usually the only step is to download all your data from Bitvavo and import them to Koinly. There are a few ways you can do this:
If you want to use CSV files, you must make sure to import your deposits/withdrawals and trades for ALL years - not just the current one!
That's pretty much it. The only other thing to be vary of is to tag your airdrops/forks so they appear as Income on your generated cryptocurrency tax reports!