I agree with Degemme's response below that I do not want to create a journal entry to correct this imbalance without having it attached to the specific product in the inventory management system. After sitting on hold with the Quickbooks customer support team for approximately 2 hours, I have learned why the Quickbooks Online version does not allow this type of adjustment.

Since Quickbooks Online uses the first in/ first out (FIFO) method of calculating inventory value (as opposed to the average cost method) it does not allow users to adjust inventory value for a specific product by direct adjustment. It only allows users to adjust product quantity (unless you want to adjust said product's starting value, which most of the users on this post, understandably, did not want to do).

After spending some time reviewing some of the products of concern for our company, I realized that most of the asset value errors I was seeing in our inventory valuation summary report were caused by doing inventory quantity adjustments out of order. For example, completing a count for a particular product or item and then making an adjustment that I thought was correct before then selling more product than Quickbooks now thinks I have on hand (say, because said item had been taken off the shelf and was being used by our repair team and therefore not visible before the count had taken place but was still actually in our possession). Most of these issues were reflecting inventory count & adjust timing errors. So... what to do now?

What I ended up doing was going back through each item that I had this error with and using the "run report" option under the "action" choices. Then, once I had identified the specific point in time where the items valuation had gotten off (which, for our company, was typically related to a bad quantity adjustment journal entry) and then opening that journal entry and either deleting it or adjusting the quantity correctly.

My only continuing hesitation with this method of correction is that it causes me to go back in time in my books to periods that are, essentially, closed. I guess that's why it's important to include an inventory asset review at the end of every month and I'll have to be more attentive to this issue in the future.