I updated to OpenCore 0.6.8 from 0.6.7. Thanks to
@CaseySJ and
@miliuco's
thread, here are the steps to upgrade from 0.6.7.

As per the
OpenCore Update Guide, mount your macOS installation drive's EFI partition. Copy the EFI partition's EFI folder to the Desktop. Unmount the drive's EFI partition.

Get a USB thumb drive from which we'll boot our new 0.6.8 configuration before installing it in our macOS drive's EFI partition.

For a new USB thumb drive, format it with the macOS Disk Utility as Format: MacOS Extended (Journaled) and Scheme: GUID.

For an existing formatted USB thumb drive, mount the EFI partition, remove its contents to the trash and empty the trash.

Mount the USB thumb drive's EFI partition. (Remove any EFI folder from the thumb drive if one is present.) Copy the installation drive's EFI folder from the Desktop to the USB's EFI partition.

Download the OC 0.6.8 package file
here.

Now, update the EFI folder as per the OpenCore Update Guide's Step 3. After doing that, don't reboot yet.

Update all your kexts in the EFI/OC/Kexts folder.

Replace the thumb drive's EFI/OC/Resources/ folder with
@CaseySJ's Resources folder which I've attached to this post. (It contains new required images.)

For our Creator, we need to add a new
AppleInput section in UEFI of our config.plist file. We have to add the key values in the AppleInput section:

AppleEvent --> Builtin

KeySubsequentDelay --> 5

PointerSpeedMul --> 1
XML:
<key>UEFI</key>
<dict>
<key>APFS</key>
<dict>
<key>EnableJumpstart</key>
<true/>
<key>GlobalConnect</key>
<false/>
<key>HideVerbose</key>
<true/>
<key>JumpstartHotPlug</key>
<false/>
<key>MinDate</key>
<integer>0</integer>
<key>MinVersion</key>
<integer>0</integer>
</dict>
<key>AppleInput</key>
<dict>
<key>AppleEvent</key>
<string>Builtin</string>
<key>CustomDelays</key>
<string>Auto</string>
<key>KeyInitialDelay</key>
<integer>0</integer>
<key>KeySubsequentDelay</key>
<integer>5</integer>
<key>PointerSpeedDiv</key>
<integer>1</integer>
<key>PointerSpeedMul</key>
<integer>1</integer>
</dict>
NOTE: These changes are necessary so the mouse and keyboard will behave as you would expect in OpenCanopy.

Then set Misc -> Security -> AllowSetDefault = 1 so as to allow "cntrl + enter' in the picker to make selected boot option the default.

Lastly, delete the following items:
AppleEvent needs to be removed from
UEFI --> ProtocolOverrides
KeyInitialDelay needs to be removed from
UEFI --> Input
KeySubsequentDelay needs to be removed from
UEFI --> Input

Save your config.plist file, and reboot to your macOS disk using the USB thumb drive. (I had to select the thumb drive as the boot disk in the BIOS. Then, resetting the NVRAM, after which I booted successfully into my macOS installation.

If you booted successfully into your macOS installation, then mount the USB thumb drive's EFI partition. Copy the USB thumb drive's EFI folder to the Desktop. Unmount the USB thumb drive's EFI partition.

Mount your installation drive's EFI partition. Rename it's EFI folder to something like "EFI-067" and zip it. Copy the EFI folder from the Desktop to your installation drive's EFI partition.

Now reboot into your installation drive. Be sure to change the boot drive in your BIOS to your installation drive from the USB thumb drive.
Done!
Special thanks to
@CaseySJ for the information to update the Creator.