Merging two surfaces into one

Hi, I have a topography surface and I had cut out a bit of it to edit and I am trying to merge it back together. I have tried using mergesrf or blendsrf and it doesn’t work. Is there any way I can achieve this?

Attached is my rhino file:
Merging 2 surfaces.3dm (806.9 KB)

Thank you for your help

Command: _Untrim