This guide assumes that you have access to the following:
The 24-word recovery phrase of your Celo address
Recover your Celo address on the Ethereum network:
Download MyEtherWallet for Desktop (It is recommended to use the Desktop version over a webapp version)
Click on "Access My Wallet"
Click on "Access By Mnemonic Phrase"
Enter the 24-word recovery phrase for Celo
You should now have access to the same address on Ethereum, where you can recover the Ethereum you accidentally sent to your Celo address.