Support for Netgear R6900 (AC1900 smart wifi Nighthawk)?

I didn't seen support for R6900 but I did see support for model numbers that are near to R6900, such as the R6800:

Should I just use the procedure for R6800?

Thanks In Advance.

No. A similarity in the model number does not indicate that the hardware is similar - in fact, Netgear and other vendors are known to completely change hardware even between revisions of the same device.

A quick check on wikidevi for your R6900 reveals that v1 is Broadcom-based, while v2 is Mediatek-based. The v2 is probably easier to support.

NB: Never try to flash a firmware for a different device if you don't have at least serial console attached to be able to recover your device. Depending on the device, there might not even be a recovery mode.