You cannot yet claim gift aid through the app.
For tax exemption, you will need proof of donations/receipts. We are working on making this feature available.
In the meantime, you may use the transaction statement of your donation. You may access the donation transaction statement by heading to 'Contribution' tab in 'Donations', scrolling down to the donation transactions, tapping on the transaction, and then tapping on 'Statement' to generate the statement.