The easiest way to transfer files from one hard drive to another is to use a hard USB transfer cable.
You can transfer files from one computers hard drive to another by plugging in a USB file transfer cable and installing any software needed.
Then follow the prompts or instructions that come with the USB file transfer cable.
You can also use a USB cable that plugs directly into the hard drive and also powers it and then connect it to USB on your computer.
The use the copy and paste function in your computer and copy the files from the current drive to the second drive that you want the files transferred to.
If the hard drive is an external hard drive, plug it into the computer and if it's an internal hard drive ensure that it is properly connected and detectable.
Then Open the file explore by clicking the folder icon on the taskbar or search for file explorer.
If moving large amounts of data it's a good idea to use some file copy software utility instead of just the built in file copier as it will be much faster.