Can I restore the deleted Dashboard,collections

My Machine crashed, so I reinstalled the Metabase through Docker. I'm using the same Mail ID and Password to log in but my previous data is not available how do I retrieve that?

Not with Docker. That's how it works when you don't have persistent storage.

Put it down to experience and have a proper database (Postgres ideally) as the backend this time.

On the plus side, if you'd upgraded to a new version in 6 months time, you'd have lost another 6 months of work.

through Postgres how can I save the dashboard and collections?

Postgres stores all the Metabase data instead of using the H2 database that's installed within the container by default. Docker containers aren't persistent, so updating just starts all over again.
If you store everything in Postgres to start with, you just tell the container where to connect to.
PS. Don't use Docker for a database unless you understand how to make the data persistent.