Orbit RBR20 - Slow Wifi

Problem: ISP plan was upgraded to 1000M, but wifi could not reach the promised speed

Recently I changed my plan from 300M to 1000M.  I tested the speed using wired desktop and the speed was able to reach the promised speed 915/903 (download/upload).  I also tested the speed of the Orbi router using the in-app speed test feature while the router was connected to the ISP modem, the speed was fine to me 906/883 (download/upload).  However, the wifi speed I tested was only 415/252 using iphone XR and closed to the primary router; it was even slower when connecting to the satellite (296/379).

When it was 300M plan, the wifi speed is close to 300 (241/286).  The working environment is the same, i.e. 3 to 4 devices are connected.  The only changed factor is the ISP promised speed.  What is the cause of the problem here? and what can I do to improve the wifi speed to close to the promised speed (1000M)?

Router model: RBR20 with one satellite

Firmware Version: V2.7.3.22

Thanks & Regards