Welcome To AndroidCentral! Hopefully we can get you sorted.
Could you let us know what phone you have?
There are various different ways to get the settings icon back depending on the phone you use. You can always swipe down once or twice (depending on the phone) from the top of the screen and tap the little Circle COG icon in the top right corner to get back into your settings.
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Welcome to Android Central! What do you mean by a "temporary power failure"? Do you mean the phone shut down due to a drained battery? Are you saying you don't see the Settings icon in your App Drawer?
I've never heard of Remni. Do you mean Xiaomi Redmi?