I sent USDT from one MM account to my other one I have (same wallet, 2 different accounts)
One is BSC and other Is ETH main net…
I sent to the ETH wallet and from the BSC one without realising the difference at the time and the USDT never showed up…
How do I get it back?
Open your Metamask ETH mainnet accounts and switch on BSC 
+ add USDT token
add USDT contract address: 0x55d398326f99059ff775485246999027b3197955
https://metamask.zendesk.com/hc/en-us/articles/360015489031-How-to-View-See-Your-Tokens-and-Custom-Tokens-in-Metamask
I’ve done that - still nothing
and check your ETH mainnet address on the page https://bscscan.com/ show USDT?