How to power on device without power button?

If you find a service manual… there may be information that you can use to more easily disassemble and find where the power button goes to on the board and bridge those pins with a small screwdriver or wire to try to power on. At that point you can also test and see if the power button is working… unless you totally don’t really have a power button (make sure it’s not the top part only… there might be something you can press still with a smaller tool or pencil tip).

Some makes and models have reset procedures where you have to press the power button so many times and hold down for so long. You can read into that online by searching and see if there is that info available.

If there is not power button at all… then, if you want to power on, you need to find where the power button leads went to and bridge the open circuit there to trigger the power on process.