You can change your country of nationality and residence only after you have successfully verified your KYC.
Please note your change of nationality or residence request will place your account under unverified status. Once your change request is successfully processed, you will be able to send/receive or buy/sell cryptocurrencies.
From left slider, tap on your name. Select KYC and edit option (pencil icon). You will now be able to edit your KYC details.