You did not name the brand and model number of the laptop.
You say you have two distinct hard drives, but the laptop is not set up as two distinct hard drives.
If the second HDD is partitioned, it should see more than two drives.
The problem is likely in the drivers being all on one of the drives and bios accesses that drive to boot up.
The Windows 7 operating system may not be compatible with the laptop systems drivers.
I cannot see the purpose of booting Windows 7 if you have Windows 10.
i7-8550U and its compatible core logic needs special hacking to run Windows 7
https://pressf1.pcworld.co.nz/showthread.php?147470-How-to-install-Windows-7-on-8th-Generation-Intel%AE-Core%99-i7-8550U-Processor-Solved
This is for advanced software people only.
Your bios is not user accessible if you need that accessed.
I know a lot about hardware and understand software issues, but not to the level you need it with that laptop.
Good luck and hope you don't mess up your laptop trying to F around with an operating system going obsolete.