Setting Normal Map to one specific Uv channel within the material

Hi, I’m having problems applying a normal map to one specific uv channel. I can’t use two seperate materials for the different parts of model I can only use one. The model will be used in unity then uploaded onto a mobile app. Please see the images below.

I only one want the normal map to be applied to the uv channel 1 highlighted in green.

Many Thanks

Does unity do multiple UV maps?

Can you make your two UV maps into one?