There is no legitimate or "free" tool that can automatically bypass or "open" a Privatter password. Privatter is a Japanese platform used primarily by artists to share content (often fanfic or art) with specific groups or followers.
If the block is language-based, use or Google Translate extension to read the public part of the blog. Many Privatter users leave the first paragraph unlocked. privatter password opener free
Politely ask the creator: "Could you post an unlisted Imgur or Pixiv link for your non-Japanese followers?" Some will oblige. There is no legitimate or "free" tool that