It will only credit if United is your selected airline. Here is the link to UTB
https://www.united.com/en/us/fly/account/travelbank.html
No need to set anything up, just go to the link, log in with your United credentials, click fund my travel bank. It may make you sign in a second time. Select the purchase amount of $100. Add the card you wish to use to pay and associated details, then click purchase now. Do it a second time for another $100. Repeat the same thing in January. Within a couple of minutes you will have it loaded. When you are logged into your account you will see how much is in your travel bank to use.
Here is a pretty decent article on United Travel Bank
https://www.nerdwallet.com/article/travel/united-travel-bank-what-to-know