ASUS UEFI Harddisk Boot Priority

Windows 10 Pro 1909 was originally installed in a 500 GB hard disk.Since the hard disk was giving trouble recently a 1 TB disk got installed and shifted the os but retained the old one for storage..When some updates were not able to install did sfc scannow which returned that resource could not be opened or whatever.Then did "DISM retsore" health which returned "fatal hardware fail".tested the 1 TB hard disk with seagate tools and it failed long generic Backup done with Macrium Reflect which returned MFT error 6 which could not be fixed by DISKCHK.So I decided to shift the os to old drive for removing the new one for repairs..Cloned the os partition and now OS in old disk boots as long as new disk partition remained in place.Then able to install updates and upgraded to 1909..
Now i wanted to change the boot priority from new to old but old disk is missing in boot priority 1 or 2.Kindly advise me how to change priority.I have attached two images of bios..thanks

Does the disk show in the bios? Is the disk bootable or are boot files on the other drive?

Yes sir The disk is shown under heading information and also and also in boot menu

can you post a screenshot from disk manager showing all the details of all disk

Attached the screenshot as desired

That doesnt look like its running in UEFI mode. Looks like standard MBR type. With UEFI you have additional partitions. Things just look abit screwed up thats all.

For a dual boot UEFI system on two seperate hard drives unfortunately you are going to have to start again. Making sure the C drive which you are using right now is the 'Active' partition, otherwise it doesnt know where to go, like driving to a destination without a satnav these days.
Removing any logical partitions for now would help with the process. So two blank drives without any 2nd partitions would be a great start
Looks like the drive letters are also abit messed up.

First step then as a test. Go into BIOS and then the BOOT tab, then disable the CSM. Reboot machine and see if you can see either of the hard drives. If not then we now know the HD's are in MBR format, not GPT. If that is the case, then the same applies. Active partition and C drive need to be in the same space. Thats what i reckon anyways.
Good luck chap. If i am wrong in any way here accept my dumbness

Yes missing the UEFI partition (100mb). Clone didn't work.

Follow Pluginz directions.

I disabled CSM and no boot is visible.Will follow suggested remedy thanks