How can I search specific transactions?

The easiest way is to navigate to the 'Transactions' page via the hamburger menu. In the search field (in the header) you can search and filter your transactions by counter party name, account number, transaction amount, comments and tags (in case you added these to your transactions via the 'booking detail').

If you have multiple bank accounts linked to OkiOki then the 'My bank accounts and cards' page gives you a consolidated overview of all your bank transactions. Here you can also find your credit card expenses in case you added your credit card statements to OkiOki.