suvid: Yes, the way to update the schema is to create an update script as you found out. You can run the `psql` command line tool to run that script file (-f option https://www.postgresql.org/docs/current/app-psql.html#APP-PSQL-OPTION-FILE), either on your own machine or from inside the docker container (`docker exec -it container-name bash` to get a prompt in the container). Don't forget to also update the `create_tables.sql`, `create_foreign_keys.sql`, etc. with your changes.

However I am not sure you need a new table for these events. If I missed something let me know.
The `user_timeline_event` table has a `metadata` columnn in JSONB format, which allows us to attach extra information to events. It is used for example to add a `blurb_content` (some text) to a personal recommendation between users.
I think the thank you event could just be a new type of user_timeline_event with `blurb_content` (like for personal recommendations, see https://github.com/metabrainz/listenbrainz-server/blob/master/listenbrainz/db/model/user_timeline_event.py#L52-L54), and an additional `original_event_id` and maybe an `original_event_type` (not certain that would be needed).
It might also make sense to store more information such as the name or user_id of the original_event creator, for convenience, but I'm not sure of that.
Then look at https://github.com/metabrainz/listenbrainz-server/blob/master/listenbrainz/db/user_timeline_event.py#L117-L154 and same file lines 205-252 for an idea of how to implement the server endpoints for creation and retrieval fo the events.