So, lets take

download-pex-bin

for example. You'd then ask for

./pants help-advanced

for that tool:

$ ./pants help-advanced download-pex-bin

`download-pex-bin` subsystem options
------------------------------------

The PEX (Python EXecutable) tool (<https://github.com/pantsbuild/pex>).
 
Config section: [download-pex-bin]
 
None available.

`download-pex-bin` subsystem advanced options
---------------------------------------------
 
  --download-pex-bin-version=<str>
  PANTS_DOWNLOAD_PEX_BIN_VERSION
  version
      default: v2.1.54
      current value: v2.1.54
      Use this version of pex.
      
      Supported pex versions: >=2.1.51,<3.0

  --download-pex-bin-known-versions="['<str>', '<str>', ...]"
  PANTS_DOWNLOAD_PEX_BIN_KNOWN_VERSIONS
  known_versions
      default: [
          "v2.1.54|macos_arm64|c892c82961f73e41aaafad3c692cfd51f6013bed2f7b408041be6c1b90d06451|3679238",
          "v2.1.54|macos_x86_64|c892c82961f73e41aaafad3c692cfd51f6013bed2f7b408041be6c1b90d06451|3679238",
          "v2.1.54|linux_x86_64|c892c82961f73e41aaafad3c692cfd51f6013bed2f7b408041be6c1b90d06451|3679238"
      ]
      current value: [
          "v2.1.54|macos_arm64|c892c82961f73e41aaafad3c692cfd51f6013bed2f7b408041be6c1b90d06451|3679238",
          "v2.1.54|macos_x86_64|c892c82961f73e41aaafad3c692cfd51f6013bed2f7b408041be6c1b90d06451|3679238",
          "v2.1.54|linux_x86_64|c892c82961f73e41aaafad3c692cfd51f6013bed2f7b408041be6c1b90d06451|3679238"
      ]
      
      Known versions to verify downloads against.
      
      Each element is a pipe-separated string of `version|platform|sha256|length`, where:
      
        - `version` is the version string
        - `platform` is one of [linux_arm64,linux_x86_64,macos_arm64,macos_x86_64],
        - `sha256` is the 64-character hex representation of the expected sha256
          digest of the download file, as emitted by `shasum -a 256`
        - `length` is the expected length of the download file in bytes, as emitted by
          `wc -c`
      
      E.g., `3.1.2|macos_x86_64|6d0f18cd84b918c7b3edd0203e75569e0c7caecb1367bbbe409b44e28514f5be|42813`.
      
      Values are space-stripped, so pipes can be indented for readability if necessary.

  --download-pex-bin-use-unsupported-version=<UnsupportedVersionUsage>
  PANTS_DOWNLOAD_PEX_BIN_USE_UNSUPPORTED_VERSION
  use_unsupported_version
      one of: [error, warning]
      default: error
      current value: error
      
      What action to take in case the requested version of pex is not supported.
      
      Supported pex versions: >=2.1.51,<3.0

  --download-pex-bin-url-template=<str>
  PANTS_DOWNLOAD_PEX_BIN_URL_TEMPLATE
  url_template
      default: <https://github.com/pantsbuild/pex/releases/download/{version}/pex>
      current value: <https://github.com/pantsbuild/pex/releases/download/{version}/pex>
      URL to download the tool, either as a single binary file or a compressed file (e.g. zip file). You can change this to point to your own hosted file, e.g. to work with proxies or for access via the filesystem through a `file:$abspath` URL (e.g.
      `file:/this/is/absolute`, possibly by [templating the buildroot in a config file](<https://www.pantsbuild.org/v2.9/docs/options#config-file-entries))>.
      
      Use `{version}` to have the value from --version substituted, and `{platform}` to have a value from --url-platform-mapping substituted in, depending on the current platform. For example, <https://github.com/.../protoc-{version}-{platform}.zip>.

  --download-pex-bin-url-platform-mapping="{'key1': val1, 'key2': val2, ...}"
  PANTS_DOWNLOAD_PEX_BIN_URL_PLATFORM_MAPPING
  url_platform_mapping
      default: {}
      current value: {}
      A dictionary mapping platforms to strings to be used when generating the URL to download the tool.
      
      In --url-template, anytime the `{platform}` string is used, Pants will determine the current platform, and substitute `{platform}` with the respective value from your dictionary.
      
      For example, if you define `{"macos_x86_64": "apple-darwin", "linux_x86_64": "unknown-linux"}, and run Pants on Linux with an intel architecture, then `{platform}` will be substituted in the --url-template option with unknown-linux.


`download-pex-bin` subsystem deprecated options
-----------------------------------------------
 
None available.

That gives you the details of which options to set.