Add the theme to your book's configuration book.json or book.js:

{
    "plugins": [
        "theme-seer"
    ],
    "variables": {
        "theme-seer":{
            "versionOptions": [
                {"text": "3.3","value":"/3.3"},
                {"text": "3.2","value":"/3.2"}
            ]
        }
    }
},

Install by command:

gitbook install

plugins: [
    '-sharing',
    "-fontsettings",
    'back-to-top-button',
    "copy-code-button",
    "cuav-chapters",
    "heading-anchors",
    "theme-seer"
    //...
]

Enjoy!