install Firmware or MCU

[prodat]

Hello
I have the following car radio
Pumpkin model S07

S / N f801060614031d0b07df0a5133504b52
MCU MTCB-KLD6-V2.90
Android 4.4.4_29032016
Kernel 3.036+
Build rk3188-eng4.4.4 29032016. 17:20:05

bought on ebay 2016

Problem: The Return key on the left Display-Side does not work anymore
(on display left side KEY ON / OFF OK
Volume + OK
Volume - OK
Home OK
Return ERROR no function)

have already reinstalled firmware - but no success
would now like to reinstall MCU but find no File MTCB-KLD6-V2.90
can there be errors in the MCU?
If so, please provide me a new MCUs.
Best regards
Benedikt

[Jammy]

Hi,
please first tell me your order number in amazon or buyer id in ebay,Pumpkin or AliExpress so that we can confirm more information about your unit and provide you positive solutions .
Could you show me an video about your issue?
I don't understand well which touch place you pointed to .
Regards