Okay, start in Zorin and then we take a Look at the Following:
You open Nautilus (the files Manager called ''Files''). There You click on ''Other Places''. this is the last Point on the left Side:
Please don't be irritated by the Language. My system is in german. It is the black marked Option at the Bottom. Then you get at the left Side an Overview. Take there the first One:
That should be Your current using Zorin System. When You have clicked on it, go to boot and then to efi and then You have to type in (2 times) Your Password because this Folder is secured. Then You should find something like this:
There You go in the EFI Folder. In my Case it looks like this:
In Your Case it should look different. Make a Screenshot of this and post it here so we can take a Look at this.
Sorry, here I made a Mistake. I mean Pop OS not Zorin. Because you want to remove Pop OS. I will correct that.