cp terraform.template.tfvars terraform.tfvars and modify that new file accordingly or provide variables via CLI:
terraform apply
-var="prod_access_key=AAAAAAAAAAAAAAAAAAA"
-var="prod_secret_key=SuperSecretKeyForAccountA"
-var="test_account_id=123456789012"
-var="test_access_key=BBBBBBBBBBBBBBBBBBB"
-var="test_secret_key=SuperSecretKeyForAccountB"
-var="bucket_name=tf-bucket-in-prod" \