I’m not sure I understand what’s happening here. It sounds like you have a PC with 2 hard drives, the first has windows on it and the 2nd you tried to install PopOS over zorin. Can you boot into windows? It looks as if you can’t boot into PopOS? Did you erase the old partitions and completely set a new partition of the hard drive when installing PopOS or did you try to preserve it and install PopOS along side zorin on the hard drive.
You should be able to select your windows drive to boot from in your bios. If you can, and I’m assuming you are more confident with windows, then you can use disk manager to destroy the partitions of the drive you installed PopOS onto and try re-installing it. PopOS is really simple to install and use. If you are getting the grub error message when trying to boot from the windows drive then grub might have been installed on that drives EFI partition.
I had a similar problem the first time I installed linux. Although I installed it on same drive as windows. The newly installed boot loader would not let me run windows after I destroyed the linux install. I fixed it by reinstalling the linux distro that installed the grub bootloader (zorin in your case). This allowed me to boot into windows again. Then I followed the steps listed here. This wiped out grub and I was able to install the next distro along side windows.
I hope this helps. I know I was feeling a little helpless when this happened. If you continue to have problems then I would try using a windows install usb and use the repair install option. I believe it should repair your original bootloader without losing anything from your windows install.
But a word of warning. After using PopOS for about a month, I found that I had mostly stopped booting to the windows side.