I did some more thinking about this and the thought dawned on me: low blood pressure is a symptom of being unhealthy, so anything "healthy" may help reverse it. That's when I thought of exercise. Of course, exercise is a great way to lower blood pressure when it's too high. But exercise is healthy, so maybe it could help address low blood pressure, too? After doing a little digging, it appears exercise can help with low blood pressure.
Interestingly, weak calf muscles can be a contributing factor to low blood pressure, because apparently the soleus acts as a "second heart" to pump the blood back in return up to the heart. Strengthening the calves can therefore help to reverse low blood pressure.
You may suggest exercise, especially things like brisk walks uphill.