Restart Fastlane::BuildWatcher and call Pilot::BuildManager.new.distribute

Fastfile

# fastlane watch_and_dist
# or
# fastlane watch_and_dist username:"your@email.com" team_name:"Team Name" app_identifier:"com.your_app" version:"1.1" build_number:"239" groups:"Group1,Group2"
lane :watch_and_dist do |options|
  # Set ENVs for Spaceship and Pilot
  ENV['FASTLANE_USER'] ||= options[:username]
  ENV['FASTLANE_ITC_TEAM_NAME'] ||= ENV['FASTLANE_TEAM_NAME'] = options[:team_name]

  # Prompt for needed app/build info
  app_identifier = options[:app_identifier] || UI.input("App Identifier")
  version = options[:version] || UI.input("Version")
  build_number = options[:build_number] || UI.input("Build Number")

  # Prompt for groups
  groups = options[:groups] || UI.input("Groups (comma separated):")
  groups = groups.split(",")

  # Login to spaceship because we need to find the app
  fastlane_require 'spaceship'
  Spaceship::Tunes.login
  Spaceship::Tunes.select_team

  # Find app and wait for processing
  app = Spaceship::Tunes::Application.find(app_identifier)
  build = FastlaneCore::BuildWatcher.wait_for_build_processing_to_be_complete(
    app_id: app.apple_id,
    train_version: version,
    build_version: build_number
  )

  # Distribute build to external testers
  fastlane_require 'pilot'
  config = {
    app_identifier: app.bundle_id,
    
    distribute_external: true,
    groups: groups,

    # Need this
    notify_external_testers: false,
  }
  Pilot::BuildManager.new.distribute(config, build: build)
end