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 tap deposit.

This will move the HXD to the rewards screen inside the game.  Access the rewards screen by tapping the Rewards button in the lower left corner. Then tap the Misc. button. This will allow you to claim the deposit so you can use the funds in the game.

In-Game Bank

Tap on the main menu, then choose Bank.

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

This will move the HXD to the rewards screen inside the game.  Access the rewards screen by tapping the Rewards button in the lower left corner. Then tap the Misc. button. This will allow you to claim the deposit so you can use the funds in the game.

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

Withdrawals:

Withdrawals are manually approved and may take up to 24 hours to appear in your wallet. The frequency of withdrawals you can make is based on your VIP level. Withdrawals should be in round numbers greater than 50 HXD.