There are two ways to deposit HXD into your game account: Hivemind and the in-game Bank.

Withdrawls can only be made using the Bank. 

Hivemind

The Deposit HXD button is on the right side, just below your banner.

Choose an amount, then click deposit. This will move the HXD to your in-game wallet.

In-Game Bank

Tap on the main menu, then choose BANK in the bottom row of icons.

Choose Deposit or Withdraw, enter the amount, and click the button. You will be taken to your wallet to approve the transaction.

NOTE: If you have trouble with the in-game Bank, try using Hivemind.