This is with reference to the thread posted by syami on 2019-08-27 21:39:17.

Here is the reply from Kevin_Z from TP_Link to this thread.  

Re:I cant find firmware upgrade option - Archer C1200

@syami 

Thanks for your requesting.

From the picture attached, I found that the current firmware is a customized one for ISP's specific needs. 

If there is no firmware upgrade option, it is suggested to contact the internet service provider first. 

Solution: @syami , Once you are logged into the router, you should copy and paste this link http://192.168.0.1/userRpm/firmwareUpgrade.htm in the browser to update the firmware.