How to seed database in gigalixir?

I’m trying to redeploy an old app onto gigalixir but I’m having problems seeding the database.

In the past, the following would work:

gigalixir run -- mix run priv/repo/seeds.exs

But now when I run it, I get an error:

Attempting to run ‘priv/repo/seeds.exs’ in a new container.
[Errno 2] No such file or directory: ‘priv/repo/seeds.exs’

I also tried mix ecto.setup

Attempting to run ‘mix ecto.setup’ in a new container.
[Errno 2] No such file or directory: ‘mix’

I used to migrate using

gigalixir run mix ecto.migrate

But now that doesn’t seem to work and I have to use

gigalixir ps:migrate

How do I seed database nowadays?