It is not possible to manually change the WiFi channel on the TP-Link RE900XD extender. This device, like many WiFi repeaters, automatically synchronises the channel with that of the main router and does not offer a setting to directly change the WiFi channel from the interface or the Tether app.

Furthermore, the official documentation and manual do not mention any options for manual channel selection on the repeater. If interference or signal problems are encountered, the recommended solution is to intervene on the main router to change the WiFi channel, as the extender will automatically follow this configuration.

OK, but I have noticed that when I intervene on the router and change the channel, the TP-Link RE900XD does not follow the new setting entered in the router