Hi @sasan,
you can connect to your docker using docker exec -it -u 0 <ContainerName> bash or use your Docker Exec.
After that you can change your passwords in internal_users.yml please see here: YAML files - OpenSearch documentation
To apply changes see here: Apply changes with securityadmin.sh - OpenSearch documentation
NOTE: make sure to backup your config files before and after applying changes as all changes will be overridden according to the config files.
Best,
mj