This is the official page from which you can Download HTC Desire 620G Stock Firmware ROM (flash file) package on your Computer.
The firmware package comes as a compressed file (zip file) which contains Flash File, SP Flash Tool, USB Driver and How-to Flash Manual.
HTC Desire 620G Stock Firmware ROM (flash file)
Package Name: HTC_Desire_620G_MT6592_Asia_India_1.12.720.001_19122014.zip
Package Size: 865 MB
How-to Flash: Follow Guidelines
Firmware Link: Click Here to Get the Firmware
Package Name: HTC_Desire_620G_MT6592_Tested_25112014.zip
Package Size: 815 MB
How-to Flash: Follow Guidelines
Firmware Link: Click Here to Get the Firmware
How to Flash HTC Desire 620G Stock ROM
Step 1: Download and upzip the firmware on your computer.
Step 2: After unzipping the Firmware package, you will get the Firmware (ROM), SP Flash Tool and Driver.
Step 3: Install the provided USB Driver on your computer.
Step 4: Open the SP Flash Tool and Load the Firmware.
Step 5: Connect your HTC Desire 620G device to the computer.
Step 6: Click on the Download button to begin the Flashing process.
Step 7: Once flashing is done, disconnect the device from the computer and restart it.
Readme:
[*] Flash Tool: If you are looking for the latest version of SP Flash Tool, then head over to SP Flash Tool for Windows or SP Flash Tool for Linux page.
[*] HTC Driver: If you want to download the latest version of HTC USB Driver, then head over to the HTC USB Driver Download Page.
[*] Take a Backup: Flashing the above Firmware will delete the personal data from the device and you wont be able to recover it in anyway. Therefore, we recommend you to take a backup of the personal data before flashing the above firmware.