AWS DMS - Endpoint target Redshift with user provided S3 bucket name

DMS documentation has steps to configure custom s3 bucket https://docs.aws.amazon.com/dms/latest/userguide/CHAP_Target.Redshift.html#CHAP_Target.Redshift.EndpointSettings.S3Buckets

From console you can edit the endpoint settings and under editor in json format to add below

{
  "BucketName": "dmscustombucketforredshift",
  "ServiceAccessRoleArn": "arn:aws:iam::1xxxxxxxxxx0:role/dms-access-for-endpoint"
}

make sure the role used has permissions to bucket similar to managed iam policy AmazonDMSRedshiftS3Role