Stuck with usdt

Hi Guys,

I`m new in crypto world. Could you advise me how can i transfer USDT ERC20 and USD KCC to one USD ERC20 with minimum fee? How can i caluclate how much need ETH for transfer 70 USDT KCC to USDT ERC20? or maybe all usdt to some exchange then trade both for other coin?

my goal is to buy coupon in bitrefill but they accept only DASH, ETH, USDT ERC20 or TRC20/

Please help.