@Pepejl, welcome to the forum.
There are 3 - PCI Express 2.0 x1 slots on the motherboard. Here is an adapter card that should work for you. StarTech makes very good products. If you want more help, you can contact their Tech Support. I like to use their Chat Live option. They have always been very helpful for me.
Please click the Thumbs up + button if I have helped you and click Accept as Solution if your problem is solved.

I am not an HP Employee!!Intelligence is God given. Wisdom is the sum of our mistakes!!