Manuel enter past data in the long-term statistic datebase

I recently started tracking my water consumption via Home Assistant. Is it possible to manually enter data retrospectively in the long term-statistic? I have written down the water consumption via Excel for one year. I would like to get this data into the database somehow.

Is this possible somehow?

Not possible at the moment.
You can search for historical in the feature request forum and then vote for the suggestions there.