Create USDT Wallet on ERC20 Dart

Question

I want to understand for myself how to generate USDT ERC20 wallet in dart language. I found the web3dart library. But what does it take to generate a koschel using the 12-word phrase provided by the bip39 library? And I don’t understand, is it necessary to write a smart contract? I would like to see a small code example of how to generate a wallet. Many thanks.

Update:

I seem to have managed to generate a wallet. But how to make exactly USDT on ERC20?

var random = Random.secure();
var mnemonic = 'obvious width mechanic wheat cargo toe bike seek spirit jungle enlist thumb';
String mnemonicToSeedHex = bip39.mnemonicToSeedHex(mnemonic);
EthPrivateKey credentials = EthPrivateKey.fromHex(mnemonicToSeedHex);
Wallet wallet = Wallet.createNew(credentials, mnemonic, random);
var address = await credentials.extractAddress();
dev.log(address.hex);