Surface desing- smooth radius corner

Hello,

I've an imported surface, that I need to make some changes.

Initial state

desired state

Generally in other CAD system (for example CATIA). I could do the follwing.

Make a copy of the edges, and them make a translation to them.

Then, make a spline between the translated edges, and make a trimfinally, wtih the fill surface command, I pick the border of the surface, make a tangencial constraint between the original surface, and the new one, and the surface is closed

Now I need to replicate those steps in Creo, but I don't know how to do it. Remember, i'm working with imported stp files, all the surfaces are dead.