Power button is lost please any suggestions

I lost the power button on my Redmi Note 8, used it for 6 months somehow, and then went to a mobile shop and he said the same thing. I went to 3-4 other shops and one guy changed the power button for 120/- and it worked fine.

Try some other shops, you will get button.

Ask for some workaround they can salvage old phones parts for this.

Recently my samsung phone had constant reboots issues due to failed wifi chip. Authorized service centers said that mother board must be replaced and they didn't have the stock. I asked small road side shops, they did replace the wifi chip and my phone is working again.

So, in your case too, enquire in more road side shops, defenitely they can replace it.

Go to any good carpenter shop and ask him to make a wooden power button and attach it with proper adhesive.I did it for my old Gionee P4 phone 4 years ago.It's still intact 😁😁

Take some plastic card and cut it in your power button's internal size. Stick 2-3 peices together to make the button appear outside of phone body. 

my phone power button stopped working 2 years ago, I use schedule on or off from settings to power off & on my phone.

you omitted the most important detail, which phone is it?

If your phone is still on then you can use the Power Menu app to get all Power options

Use double tap feature on lockscreen to turn screen on/off (if it's supported). Some new android versions provide option to access power option from status bar directly. 

Find some shortcut/app to simulate power button functionality.