A Redelegate option has been added to the app to allow a user to move their staked LUNA to a different validator. Redelegations can only be done once every 21 days.
On the LUNA wallet screen, tap on Stake. Scroll down and then tap on Redelegate.
Select a different validator by tapping on the To Validator field. Tap on Next to proceed.
Before you procced, please make sure you have set the correct validator. You can only make this change once after 21 days. Tap on Confirm to submit the transaction.
Once the transaction is confirmed on the Terra blockchain, the new validator will now be shown on the Staking status.