Not specific to an A31 but I have bought several cables for my tab A7 which have usb-c at one end and something else at the other e.g. ethernet port, standard usb-a. Note you might have to look out for something which has several connections including a usb-c port which allows charging as you will want to charge while using the hdmi at the same time. I have one, not tested yet .Apart from on-line, I bought mine from either Target or Kmart, can't remember which. Watch out for over-heating.
Good afternoon @GWS22, were you looking to cast content from your phone to your TV?
Unfortunately the A31 is not MHL compatible as per our specs page and cannot stream content via HDMI. An alternative I can suggest is using 3rd party products such as a Chromecast as it is compatible with a variety of media streaming apps.
