Boardman Bottom bracket cable guide

I’m trying to replace my rear shift cable on my 2019 Boardman SLR 8.9c

When trying to undo the cable guide under the bottom bracket, the nut just spins. I’ve tried a few taps to see if I can just reseat the bolt but no luck.

Am I going to have to do this without removing the guide?

Thanks for your help!

by ajs147