Go to this link https://core.telegram.org/api/obtaining_api_id and login with with the phone number regitered on telegram.
You will get the API ID and API HASH.
Run the python script and enter your api id, api hash and phone number(with country code).
It will show you all the groups you are member of.
Select the group of which you want the members and the script will do the rest.
You can view the members scraped in a CSV file.