Accessing other account via external HD

MacBook Pro (13-inch, Early 2011)

El Capitan v.10.11.6 (15G31)

So to summarise what I have gone through, I had a kernel panic when logging into any account. So I tried to fix it by zapping PRAM and NVRAM, tried the SMC reset and both didn't work. So I've installed El Capitan on my external HD and it's working, I just need to access the other account on the Mac to retrieve the photos and then do a clean install to fix.

The problem is that I do not know how to access the other account on this mac as I haven't transferred any info from the other acc to my external HD. Is there any way to do this other than reconfiguring my ext HD and going back to the installation process again? Or am I able to get the photos on the other account through the Photos software?