I'll bite: It depends on the amount of bend, or the radius. I assume you mean bend the outwales to the shape of the shear up to the stems. If you are bending 'wales for a guide or 50 pounder, it's easier. An otca, HW, or Charles River, Like I just finished, is harder.
Consider soaking for several days. More for kiln dried. Less for fresh cut. A jig, form, or fixture for bending is the same as for a stem, more or less. I make two, one for each end and do the whole thing at once. I also make it double wide so both outwales are done side by side. Make the radius a little tighter to allow for springback.
The form has to have a way to hold the end as you bend it over the outside of the radius. AND a metal strap/band should be on the outside of the gunnels to hold the wood and help it not to split. The form may only be 3 feet long depending.. After an hour of steam/boil, then put the end in the form under the part you made to hold it down (rather than try to use a clamp on the end). Bend the rail down as the wood gives, don't go faster than the wood wants to. Once it's all the way down, then clamp the gunnels at the inboard end of the form. You could get fancy and fasten ears to the form and have holes thru the ears and put dowels through as you bend it down. I wish I had a photo but I can't find any.
For a flat sheer, I fasten at the middle and work my way out to the ends, steaming as I go. I use flexible, collapsble sewer hose from the camping section of the big box store. I boil the water and direct the steam into the end. the sewer hose is like an accordian and is slid back out of the way as I work my way from middle to end. Of course you have to do it four times.
It's probably alot easier to see it than to decifer my written instructions. Ash is cheap so don't fret if you break the first try.
