You need to have enough bandwidth and energy if you want to swap your USDT TRC20 to TRX, since you can't swap it, this mean you don't have any bandwidth and energy to proceed the transaction [1]. You need to stake TRX in order to get it or you can bought TRX from someone or exchanges.
And if you do not have an account on the exchange platforms, you can post a topic about your desire to exchange one of your currencies for TRX coins in the
[Currency exchange] section of this forum, and you will find someone to help you. If you need more questions, do not hesitate to post them here.
Only less people want to trade altcoins and it's very low volume on there, in order to make anyone interested is overpay it, so people who think it's a benefit for them.
[1]
https://tronlinkorg.zendesk.com/hc/en-us/articles/5857412550937-How-to-Get-Bandwidth-and-Energy-