We were hosting a Gingerbread decorating contest after Christmas, and didn't have enough Icing Bag Tips! So, straight to Tinkercad. I designed 3, a crossed one a plain round one and a slotted one.
We just use gallon size freezer bags and cut a small hole out of one of the corners. Then, push these tips through till tight. The little ridge around the perimeter helps kinda lock the tip in place. Fill with icing, and squeeze! To be honest the crossed one didn't make a real difference with our home made icing because it was a bit runny. But if you make (or buy) your icing it may be thicker and actually work to make little star looking spots. I leave the decision up to you. Enjoy!