ok, so i got the solution,

1. you need to login to kibana(click on the dashboard link [OpenSearch Dashboards URL in aws console]).

2.path to open dashboard(Amazon OpenSearch > ServiceDomains > your domain name)

3. in the roles section select all_access.

4. your end path should be link this.Security > Roles > all_access > Map user

5. now in the users input past your arn user.

6. in the error copy after 'User [name=', so you copy this

'arn:aws:iam::999999999999:user/media-s3' past it into the user input and click on map.

Updated Instructions for OpenSearch Dashboards:

1. Log into AWS and go to Amazon OpenSearch Service > Domains > [Your domain]
2. Click the link for "OpenSearch Dashboards URL"
3. Now inside the OpenSearch Dashboard, go to Menu > OpenSearch Plugins > Security
4. Click "Explore existing roles"
5. Find an adequate role. The easiest is all_access. Click that.
6. Click the "Mapped users" tab.
7. Click "Manage mapping"
8. In the Users field, add the full ARN of the IAM role. This is formatted like arn:aws:iam::############:role/xxxxxxxxxx
9. Click "Map"