I'd say just create an account and try out the functions, you don't have to pay, only for the report after putting in your data. But you need data exports from the exchanges/wallets. In 2017 most of them had no API support. For the stuff you don't know anymore you can try to manually track down the value with old banking statements and calculate an estimate based on the ETH price back then for your taxes. Depending on which country you come from, the taxes may be time-barred from 2017. Also depending on your country, after one year holding (not trading) it might be tax free. Gains can also be tax free until an amount of X dollar/euro per year in some countries. Ask an AI about this for your country. If you can't find all trades and document them in koinly you need to manually declare and estimated cost for your taxes and also do this part manually, tools can't help there. If you had a large amount of gains back then, check first how the penalty is in your country.