Hey there Yorgokarna,
I apologize about the late response, thank you for being patient! Were you able to get your Chromecast connected? If not, I'd be happy to help out where I can, since I know it can be hard to get devices to play nicely! Now, here are the instruction I pulled from Mi's website:
"Put the extender near the router, turn the power on and wait for the yellow indicator light to start flashing.
Scan the QR code to install the app and follow the instructions to add the device.
When the indicator light turns blue, pairing is complete.
Now you can simply unplug and plug the Mi Wi-Fi Range Extender Pro in a location for the best signal quality and coverage in your house, without needing to configure the extender again."
Now, once you get that device up-and-running, you should be able to connect that Chromecast to the Wi-Fi network like normal.
I look forward to your response, and if you have any other questions or concerns for me, please let me know!
We haven't heard back from yorgokarna, and it's been a few days, so I'm locking the thread. As always, feel free to make a new thread if you have any more questions or concerns.
Have a good one!