If you want to change it just when you display it, you can query the data first, and then loop over it. Depending on the resultset, you may need a double loop:
foreach (Event event in events)
foreach(Review review on evemt.Reviews)
review.CreateDateTime = review.CreateDateTime.AddHours(8);
Alternatively, you can do this when you insert the data, so the data is in a more consistent state in the database.
Hope this hepls,