Hey @ra_md,
The Github worker needs to have the credentials to connect to your S3 bucket. These can be configured with environment variables for example.
More info under “Click for Amazon S3” in https://dvc.org/doc/command-reference/remote/modify#available-parameters-per-storage-type
p.s. if that’s not it you can try using dvc pull -v in the workflow to see what the exact problem is.