Software doesn't allow it. While the device does support RouterTech custom firmware, that also won't let you set it to repeater mode unfortunately. You'll need to buy another device which is properly designed for this task
Edit: I might stand to be corrected. The device runs a linux-based firmware with busybox which can be telnetted into. Maybe you can hack something together with wpa_supplicant or whatever that router uses, forcing it to be a repeater somehow... or if you're really advanced, compile your own firmware for it based on openwrt or something. Is this worth the effort though vs just buying something more modern that is specifically designed for the task? Probably not.