It's unclear what you did, on three points at least:
- where that Windows 10 came from
- how you did the install
- where it says it's Dell
To fix it: use the recovery media from Asus to go back to factory conditions. Then upgrade to Windows 10, downloaded from the MEDIA CREATION TOOL (Google that).
I replaced HDD of my Asus k52f with a hard disk from my Dell because of some issues and then installed Windows 10 on it. And now the Asus says it is Dell computer. How to make it "think" that it's Asus again?