I am new to flashing devices, so please explain in simple terms...

We tried installing Ubuntu Touch on two different Nexus 5.
Installing from Mac OS using the UBports installer.
Worked perfectly on one phone, but one of the installations failed.
Now what...
I can not start Ubuntu Touch on the phone, but can get into UBports Recovery.
But the UBports installer can not see the device when it is in Recovery.
How to I fix this?

-I have just installed Linux on a computer, if linux is better for fixing this.

Al