Do they have a hole on the bottom? If so, water it, wait a bit for it to drain some, then water again until it runs out the bottom. Once a day should be ok, but certainly check in the pm to make sure. If there's no hole, then do that and stick your finger in one of the bottom holes and see if the water is getting there.
Part of the problem with those is getting the right amount of water to the bottom plants. (And they do dry out quickly.) What some folks do with the strawberry pots (a similar set up, just not hanging) is take a length of pvc pipe, drill holes in it, and put it in the center before installing the plants. Then they water by pouring down the pipe.
Not to be a killjoy, but in general you'll get more strawberries and happier plants if you put 'em in a window box or a big pot. Those hanging bag thingys are cramped and they mess with the Perched Water Table... if you notice that the bottom plants are starting to die off, and the soil near them is soggy, pull them out and put them in regular pots. In container culture there are areas in pots that don't drain & will smother & rot the roots.
Linky goodness: https://oregonstate.edu/dept/nursery-weeds/feature_articles/physical_properties/physical_properties.html