I used this script to delete a bunch of cron emails that had built up in my inbox. You should be able to change the search params to cover anything you might want to get rid of. Note this will _permanently delete_, not just move to trash.

clean_gmail_emails.py

import pickle
import os.path
from googleapiclient.discovery import build
from google_auth_oauthlib.flow import InstalledAppFlow
from google.auth.transport.requests import Request

# If modifying these scopes, delete the file token.pickle.
SCOPES = ['https://mail.google.com/']


def _update_creds():
    creds = None
    # The file token.pickle stores the user's access and refresh tokens, and is
    # created automatically when the authorization flow completes for the first
    # time.
    if os.path.exists('token.pickle'):
        with open('token.pickle', 'rb') as token:
            creds = pickle.load(token)
    # If there are no (valid) credentials available, let the user log in.
    if not creds or not creds.valid:
        if creds and creds.expired and creds.refresh_token:
            creds.refresh(Request())
        else:
            flow = InstalledAppFlow.from_client_secrets_file(
                'credentials.json', SCOPES)
            creds = flow.run_local_server(port=0)
        # Save the credentials for the next run
        with open('token.pickle', 'wb') as token:
            pickle.dump(creds, token)

    return creds


def clean_crons(next_page_token=None, deleted_count=0):
    creds = _update_creds()

    service = build('gmail', 'v1', credentials=creds)

    if next_page_token:
        results = service.users().threads().list(
            userId='me',
            q='label:cron',
            pageToken=next_page_token,
        ).execute()
    else:
        results = service.users().threads().list(
            userId='me',
            q='label:cron',
        ).execute()

    threads = results.get('threads')

    if threads:
        for thread in threads:
            print('deleting %s' % thread['id'])
            service.users().threads().delete(
                userId='me',
                id=thread['id'],
            ).execute()
        deleted_count += len(threads)
        print('deleted %s so far' % deleted_count)
    else:
        print('done at %s' % deleted_count)
        return

    next_page_token = results.get('nextPageToken')

    if next_page_token:
        clean_crons(
            next_page_token=next_page_token,
            deleted_count=deleted_count,
        )


if __name__ == '__main__':
    clean_crons()