You could do either of these things:
Reinstall from scratch ("clean install") onto the SSD,
with the HDD totally disconnected. This will force the boot files and system onto the same drive.
or:
Copy the boot files from the HDD to the SSD.
Problem is, I don't personally know how to do the copy.
But it's simple enough and I'm sure someone here knows how. Probably using bcdedit.
https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/bcdedit
Hope they respond or do the clean install.
Even after that, I would certainly back up any personal files before doing the mbr to gpt conversion because that can go wrong and you could lose everything.