We know a lot more about DIY than any of the 132,523,923 different models of random ebike which all have parts with the original manufacturer's names removed.
Luckily you have a brand name displayed at least.
There's a total of 2 threads on this forum about the controller. That means it's very rare because we are a big forum. Hopefully you can find some information here:
Search results for query: kyesang
Do you know anything about soldering? if so, you could swap to another controller, display, other electrics. If not, it's not a difficult skill to pick up, and if you get serious into building ebikes, you will be glad you learned it.