You need to include a proper .prettierrc file in the root directory, as the docs about Prettier Configuration File says:
The configuration file will be resolved starting from the location of the file being formatted, and searching up the file tree until a config file is (or isn’t) found.
Prettier intentionally doesn’t support any kind of global configuration. This is to make sure that when a project is copied to another computer, Prettier’s behavior stays the same. Otherwise, Prettier wouldn’t be able to guarantee that everybody in a team gets the same consistent results.
root
├── app
│ ├── file4
│ ├── public
│ │ └── file5
│ └── src
│ ├── file1
│ ├── package.json
│ └── .prettierrc
├── file2
├── file3
└── .prettierrc
If you have a directory structure like above, the files under root/app/src/ (file1, package.json and root/app/src/.prettierrc) will be formatted according to root/app/src/.prettierrc config file, and other files under root/ or its subdirectories (file2, file3, root/.prettierrc, file4, and file5) will be formatted according to root/.prettierrc config file.
Or you can configure default options of Prettier for VS Code:
Configuring Default Options
Some users may not wish to create a new Prettier config for every project or use the VS Code settings. Because Prettier searches recursively up the file path, you can place a global prettier config at ~/.prettierrc to be used as a fallback.
You can also use the setting prettier.configPath to provide a global configuration. However, be careful, if this is set this value will always be used and local configuration files will be ignored.