Assign boundary conditions directly to vertical face in 3D model

I built a 3D brine intrusion model, and one of boundary vertical face can be treated as hydrostatic.
I now assign the 1st head boundary slice by slice(horizontal), but it seems time-consuming. Does a alternative approach exist to quick assignment?

In FEFLOW 6 Standard, nodes on different slices can be selected simulataneously for boundary condition assignment.

Thank you for your suggestion, i will try it on the Standard Interface of Feflow 6.