Where exactly do I put my AWS access key and secret key when using Terraform Cloud?

I am using Terraform Cloud for remote plan execution.

Where exactly do I put my AWS access key and secret key?

When running plans locally, I use AWS_PROFILE=my_profile_name terraform plan, and this uses the credentials that are saved on my computer in ~/.aws/credentials.

When I attempt this with my backend.tf setup to use Terraform Cloud, however, I get:

No valid credential sources found for AWS Provider.