Firstly just like others have said, you need to download the latest version of Electrum now if you are not used to technical stuff like Phyton and the rest then you can proceed to make use of the raw complied exe format from the original ELECTRUM website.
Seed phrases generated by blockckchain.com before their 2016 upgrade were not BIP39. Those seed phrases were non-standard, included 16-20 words and can't be imported into electrum or other wallets.
What you have to do is input the seed phrase I'm addition with the custom words separated correctly with just a single space. If it's correct then Electrum will give you a feedback that it's a valid check sum and tell you what wallet format it is.
As I said, OP can't use electrum if the seed phrase has been generated by blockchain.com before 2016.
And note that even if OP's seed phrases was supported by electrum, the passphrase (custom words) should have been entered in a different window (not along with the seed phrase).