Noob Questions: Wifi Telemetry on Matek 405 wte

I am trying to connect a Matek F405-WTE flight controller to a ground station over WIFI however I am having issues setting up the connection.
I can load regular ArduPilot firmware onto the board by holding the DFU button when plugging in by USB. However, if I load MAVESP8266 (firmware-esp01_1m) which I believe is required for WiFi telemetry (?), then I cannot connect to the board in mission planner. The manual also says to connect the Tx1 to ERx and the Rx1 to ETx, I can do this however it then stops me from being able to enter DFU mode. Additionally, the manual states to set the SERIAL1_BAUD to 921 which I can do when loaded with regular ArduPilot firmware, but because I cannot connect with MAVESP8266 I am unable to set these parameters?

How do I get this working? Is it meant to be two things flashed onto the board and if so, how would I do that?

Thank you for any help, tips or advice.

The instructions here seem pretty straight forward. Get yourself a USB-TTL adapter and use the NodeMCU flasher:
F405-WTE ESP8266

How exactly did you flash the MAVESP8266 firmware? According to the manual you can do it with a USB-TTL adapter to ERx/ETx.

Before you can configure ArduPilot so that SERIAL1 outputs Mavlink 2 with 921600 baud.

But in Mission Planner you set 115200 baud for the Wifi connection (UDP on Port 14550).