To switch the coin, you need a positive USD balance in your account.
If you need to charge up your USDT balance, we advise you to use this link: How to charge up your balance
First go to the section “MY HARDWARE”:
Now you can see your own Hardware. Choose the payment coin and that's all. The miner reconfiguration needs 30 minutes.
Note: if your USDT runs out of balance, then the miner switch automatically back to BTC, so that's your mining isn't interrupted. The same in BTC. If you have no BTC, the miner will switch to USDT (if there is a balance available). If no balance available, then the miner will get the non-profitable status, and you receive an email.