Dashboard => IAM => Access Management => User groups => [ group_name ] (.e.g. admin) => Attach permissions policies: AdministratorAccess => Create user group
Create a user:
Dashboard => IAM => Access Management => Users => Create user => User name: [ user_name ] => Next => User groups: admin => Next => Create user
Get credentials:
Dashboard => IAM => Users => Click user => Access keys => Create access key => Command line interface (CLI) => Create access key => Download csv => Done