This documentation is for the original WiFi Standing Desk Controller, not the Upsy Desky. You can tell which one you have by looking at the port it uses for flashing. If it's a micro-USB port, you have the original WiFi Standing Desk Controller. If it's a USB-C port, you have the Upsy Desky.
Firmware for the Upsy Desky is available here.
If you don't have ESPHome readily available, you can flash a pre-built firmware to your board. These binaries will advertise a captive portal on an ad-hoc WiFi network so you can connect it to your WiFi without needing to install ESPHome.
If you are using a supported browser (i.e., a Chromium-based browser), then you can flash the firmware directly from the web. Select your desk brand below, then press the big blue button. Connect the board to your computer, select it from the list, and install.
If you are not using a supported browser, or you need the raw firmware binaries, you can download them from the GitHub releases page.