I have poor wireless speed 200 mbit on 1000mbit line...

What Firmware version is currently loaded?
What is the Mfr and model# of the Internet Service Providers modem/ONT the NG router is connected too?

What wifi devices do you have and speed testing with. Some devices on 5Ghz top out or max out at around 200-500Mpbs and will never see anywhere near 900-1000Mpbs due to there 2x2 MIMO design and support. 

What is the size of your home? Sq Ft?
What is the distance between the router and 📡 satellite(s)? 30 feet or more is recommended in between RBR and RBS🛰️ to begin with depending upon building materials when wirelessly connected.

You can't change the 5Ghz channel on the RBR? What browser are you using? Try a different browser? 

What channels are you using? Auto? Try Auto and 48 on 5Ghz. Or try setting manual channel 1, 6 or 11 on 2.4Ghz and 40 to 48 channel on 5Ghz.
Any Wifi Neighbors near by? If so, how many?

Try disabling the following and see:
Armor, SPC, Traffic Meter.