If you have the correct 18-word seed phrase, you can use Electrum to restore the wallet. Make sure to download from the official site and verify it, here's a guide to help:
https://bitcointalk.org/index.php?topic=5240594.0Once you have Electrum installed, create a new wallet, select standard wallet > I already have a seed phrase, then enter the seed, then click the options button and select Bip39.
If you don't have the correct seed phrase, but you have the original email, contact Blockchain.com's technical support, they will be able to help you.
BIP39 seed phrase are 12, 15, 18, 21 and 24 words long. If it is 18 words, Blockchain.com has that before the introduction of BIP39 seed phrase.