To create IAM role using Access Keys you should do following steps.
To learn how to create access keys, see the AWS Documentation.
The user whose keys you will use to create an IAM role should have the following permissions:
"iam:CreatePolicy", "iam:GetRole", "iam:UpdateAssumeRolePolicy", "iam:GetPolicy", "iam:CreateRole", "iam:AttachRolePolicy"
The new IAM role with the required permissions you have selected will be created in AWS and will be added to Veeam Backup for AWS automatically. After that you can use this role where you require.
There are currently 3 options available: