To initiate the migration process, you must first download your Rocket.Chat database to your local system and import it into your local MongoDB server. Specify the file path of the downloaded database and the server URL for the MongoDB, along with the database name where you imported your data. Additionally, you can specify the date range for the attachment files that need to be migrated from Rocket.Chat to Mattermost. For downloading attachment files, specify the location where you want to save them.

Upon running the code, you will obtain a JSONL file and a folder containing all the shared files. The JSONL file contains user details, their messages, attachment file paths, and channel memberships with message history.

Utilize the generated JSONL file to efficiently migrate all chats to Mattermost using its bulk upload functionality.