Logging out or delete Fantasy Strike account from my Nintendo Switch

Hello! I have bit of an issue.
My problem is I created new Steam’s Fantasy Strike account because I’ll delete old Steam account. but my old account is still connecting to Nintendo Switch. So I tried delete my Fantasy Strike’s savedata on my Nintendo Switch. but I couldn’t logging out my old Fantasy Strike account.
So, I have a question. Can I logging out or delete my old Fantasy Strike account from my Nintendo Switch, So that I may switch to the one tied to my new Steam account?
(I’m Japanese.This forums is from Japanese to English translation. If you can answer it on Japanese, Please type in Japanese.)