missing core on BananaPI

Hi,

on my BananaPI I installed this image: Armbian_5.10_Bananapipro_Debian_jessie_4.5.2_desktop.raw
I followed these instructions: https://searchathing.com/?p=250 to move / to SATA (or USB) and crypt it with LUKS.

After all, cat /proc/cpuinfo says, there is only 1 CPU-core.

How can I activate the 2nd core?

Thanks for your help