My new build already has Windows 10, it's functioning and working fully. Just worried it installing an old Hard Drive with a fake copy of Windows 7 might screw up my new build. So I'm wondering how am I supposed to transfer it to my new build. It's an old hard drive with 500 GB of space
So this has stuff on it you want?
Or do you just want the bare drive?
The safest way is with a USB dock. Power up the PC with your Win 10, then connect the dock, and wipe the drive.
But...lacking a dock, you can just connect it internally, and verify in the BIOS that this Win 7 drive is NOT in the boot order.
Copy what you want from it, then fully wipe the drive. Delete ALL partitions on it. Use as desired.