If the cost basis seems off, the transaction values could be wrong. Open the Transactions page and correct the value of the asset, if necessary (instruction).
Another name for cost base in Cointracking is asset value. You can adjust the asset value of a transaction by editing them via the Transactions page where you can search for the trade. Mark the trade and click on "Edit" and afterwards on "Edit Asset value". There you can adjust it.
A case for a necessary Asset Value/Cost Basis adjustment of a trade would be, if you bought new coin (e.g. during ICO) which was not listed on coin price sources during the purchase time. In this case please open all transactions on the Transactions page and enter the sale value into the empty purchase value field:
Please note that deposits and withdrawals do not have a cost basis as they are considered movements between wallets or exchanges. That's why they will not be calculated in the tax report.