You can contact the seller from the account you have used to send your message to this forum - but they won't be able to connect this account to your guest purchase.
Why do you need to contact them?
If it is regarding your purchase, they won't be able to change the address or anything, but they will probably be prepared to answer a question.
Generally though, it's best to ask any questions before you buy and to log into your account to make a purchase.
You can't leave feedback if you buy as a guest.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)