Where should I add SSD for Herobook Air

I want to add SSD for Herobook Air. When I opened the SSD slot on the back, the SSD described as 128GB was already installed. Is this a standard 128GB SSD? So where should I add SSDs?

Hello, there is no extra slot for this model, only the original SSD can be replaced, thank you

Thank you for your reply. After that, I thought so too, and replaced the 128GB SSD with a larger capacity SSD.