Accidentally sent ETH to a Theta address
The Theta wallet can only be used to store the tokens on Theta blockchain, THETA and TFUEL. You can’t store ETH with it.
The ETH you sent to the Theta wallet address is still on Ethereum blockchain and can be accessed via an Ethereum wallet like MyEtherWallet. Since MEW and other Ethereum wallets don't use the same format of seed phrase as Theta wallet, you will just need to derive the private key from your Theta seed phrase, then use that to access the address in MEW. Here is the procedure. It might look complex, but only takes a couple minutes to complete if you follow the instructions carefully:
So first we need to take your Theta wallet seed phrase and get the private key from it. You can complete the steps involving the seed phrase and private key offline, for increased security. To do this you can use the crypto tool here:
1. In the field "BIP39 Mnemonic" enter your Theta wallet seed phrase
2. For the "Coin" field, select Ethereum
3. Go down to where it says "Derivation Path" and select BIP32
4. In the "BIP32 Derivation Path" field copy and paste m/44'/500'/0'/0/
5. If it all worked right, when you scroll down to the "Derived Addresses" section you should see your Theta wallet address and it will have a corresponding private key.
6. Take that private key and use it in MyEtherWallet to unlock that same address on Ethereum blockchain and access your ETH, and send to any other ETH address if you wish. First go to https://www.myetherwallet.com/access-my-wallet , then click Software and then Private Key, then enter that private key there to unlock the wallet
Please let us know if you have any questions/issues doing this.