Form your buns, coat with oil or spray oil, and lay out almost touching each other.
I personally use a greased 4 inch deep stainless steel Steamer tray for this. The high sides help make sides on the buns where not touching other buns.
The 4 inch deep tray is placed in a 6 inch deep stainless steel Steamer tray that contains a couple inches of hot tap water. A stainless steal Steamer tray lids goes on top. This is placed on the warm stove, This becomes the 2nd rise proofing chamber. But any successful method you use to allow the dough to rise will work.
Let this 2nd rise go 45-60 minutes or until your buns look doubled in size.