Upload/enter Reviews from other sources into a new Product Review App

When you create a Product Review App for the first time, the database behind it is initially empty.
If you switch from another review tool, you often already have existing reviews that you would like to transfer to the new app. An upload of the existing reviews (e.g. via a csv file similar to the existing export file) would be helpful for this.
You are also often listed on various B2C platforms where reviews are given for the same product. You can also enter these manually in the Product Review App on your own homepage. But then the time stamp no longer matches the original review. It would therefore be helpful to be able to change this timestamp manually in the review management environment.

In my specific example, I run my own homepage for a vacation apartment. However, I have also listed it on various travel platforms (e.g. Booking.com, AirBnB). As a result, I have reviews from my guests on various platforms, which I would also like to make available to potential new guests on my website.