Yeah. a touch screen calibration was recommended to me. I found out that the 5-finger gesture needs to be performed on the main screen after trying to perform it for several minutes in the Zlink app. My unit immediately launched the Zlink app on startup. So I had to connect a computer mouse to navigate to the main screen. Still, the 5-finger long press didn't work.I had an issue with the touchscreen not working. I contacted support via WhatsApp and they replied to me very quickly. You can try to calibrate the screen by placing and holding all fingers of one hand on the screen for approximately 15 seconds. Unfortunately, this didn't work for me, but it might work for you. In my case they sent a replacement to me within a few days, and it works perfectly.
I may have made matters worse. I performed a factory reset in System settings, and this has erased some apps like Zlink (I remember seeing a lot more app squares). After managing to change the factory-default language of Chinese to English, I still couldn't get the touch screen calibration wizard to pop up.
So I'm awaiting further guidance from the vendor.
Just documenting stuff here in case anybody encounters similar issues.