Create a user-defined policy for DAS.
On the management console, choose Service List > Management & Governance > Identity and Access Management. On the displayed page, select Permissions and click Create Custom Policy.

Select the rds:instance:list permission of RDS and das:connections:list permission of DAS.

You can also select JSON for Policy View and enter the following statements in Policy Content.

{
    "Version": "1.1",
    "Statement": [
        {
            "Action": [
                "rds:instance:list"
            ],
            "Effect": "Allow"
        },
        {
            "Action": [
                "das:connections:list"
            ],
            "Effect": "Allow"
        }
    ]
}

Create a DAS user group. Then, click Manage Permissions in the Operation column to select the custom permissions.
Create an IAM user and add it to the user group.

How Do I Grant Only the Permission to Use DAS to an IAM User?