Is the device actuallly supposed to ber able to play mp4 file format in the first place?
This suggests not:
https://www.tesco.com/direct/technika-7-portable-dvd-player-with-digital-screen-tkd7p-dvd/215-6708.prd?source=others
You could always ask Tesco - Teknika being their house label with equipment made for them by a range of far eastern manufaturing houses
acp
June 2017