Hi @ramzan
You can flash openwrt on top of padavan. It has to be done using ssh into the padavan firmware.
You will need to download the following file
There are 3 main steps to the process
1 - copy the facotry file above to the /tmp folder in the router
2 - login to the router
3 - flash using the mtd command (in padvan I believe it is called mtd_write)
If you are using windows first use winscp to copy the file to the routers /tmp folder. After that login using putty to the router.
go to the tmp folder and run the following command. This is case sensitive.
mtd_write write openwrt-23.05.0-rc2-ramips-mt7621-dlink_dir-853-a3-squashfs-factory.bin Kernel
After that the openwrt factory firmware should have been flashed to your router. After reboot you should be able to connect to openwrt.