Migration from aws managed to on-prem infra

Hi,
We are using aws managed elasticsearch service for our e-comm web application, the indexes are around 50K, and the managed service is running in vpc it is not exposed to internet, initially our whole application infra was running on aws, but for some reasons we moved our application to on-prem infra the only thing is remaining is elasticsearch which is in vpc and we are using it by creating a ec2 instance with reverse proxy in that vpc, so how we can migrate our indexes or data from aws managed service to on-prem infra ?