Easy, just take apart a front wheel and rebuild it. There are a lot of good sites that go through this step by step. Old vintage cruiser wheels usually have the same spoke length front and rear wheel, but because the rear coaster hub has a bigger diameter they use 4 cross on the rear and 3 cross on the front. If you have an old set and want to change the rim or hub you can usually use the same spokes and play musical hubs or rims. I have a ton of old spokes and nipples I have saved so I don't always buy new ones. If I have an old cruiser that I am fixing up I usually go through my junk hubs, spokes and rims and build new old ones if the originals are potato chips. You can take some dents out better by taking the wheel apart. I have taken a badly flattened old steel rim and made straight by taking out the spokes on the flat side and pitting a small bottle jack between the hub and the flat spot and then relacing the wheel. It wasn't perfect but was pretty good. I did this on a friends 1950s Schwinn American that he got new and wanted everything original. You could also start by taping a rim to an existing wheel so that the valve stem holes match and take off a nipple and bring the spoke over to the adjacent empty spoke hole. Keep doing this until the rims are changed. It is harder to do this with small wheels as there is more binding. I have even done this with good results where the rims were drilled where the holes clockwise of the stem on the rim were different (one rim had an up hole and he other had a down hole). Very often old cruiser wheels and even other wheels were built without the spokes woven under on the cross. It is faster to skip the weave so production facilities built a weaker wheel to take advantage of speed. Sometimes the factory pattern is wrong so that the wide space between spokes doesn't fall so that the valve stem is between the wide spoke spacing. Sometimes the valve stem opening is between the narrow spacing in the spoke pattern, which makes it harder to get the pump attached to the valve stem. This is wrong but the wheel still works fine. All this is easier to do and better if the rims have the hole clockwise to the valve stem drilled in the same position on the rim (either up or down from the centerline). A few rims are drill all in the center but this is rare. It's pretty easy but if you don't do it very often, like me, then you sometimes loose track and do it wrong and have to start over. I have to do it where there is no distractions demanding my attention like my dog or wife. I can no longer multi task.I can do everything with wheels except lacing.
This is the video I used when I tried relacing a couple of wheels recently. Clear and understandable and I have it saved to my Favorites now; I will probably break it out any time I want to lace a wheel for the foreseeable future.