For third party services you need to contact that third parties support directly.
If this means you had the reviews before and you imported them into the app.
That means you would be able to do so again when reinstalling the app.
Beyond that the lesson here is data ownership.
Backup data & know where the data is stored.
Some apps may use metafields to store the info directly on shopify others may store your data in externally in proprietary formats that you cannot access when done with that service.