@Joos 

The Archer A9 supports remote management, you can access it remotely via browser; 

You need enable remote management first, and the internet IP address of the A9 should be the public one, then you can access it remotely with the WAN IP and port number. 

Note: If it is private, you need open the port for the A9 so that you can access it outside. 

May it help. 

@Joos 

Connect your computer to the Archer A9, open a web browser and enter tplinkwifi.net to access the web UI. 

Then go to the advanced-system tools-administration page, and enable remote management and click save to apply the settings.

Then you can access the web UI remotely with the WAN IP( internet IP address) and port number.

May it help.