Based on some of the topics from this forum, I was able to come up with the process of customizing boot logo on my Baofeng 1702. Should work also on DM-X as they are virtually the same radio.
Process I’ve outlined in instructable -> https://www.instructables.com/Baofeng-DM-1702-Boot-Screen/
But if anyone has any questions, please feel free to ask in here, I’ll try to answer them 
Have fun!
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SO0BAD - Maciej