No need to post 3 separate threads for one question.

Without a voltage meter to test and measure the circuit breaker your only guessing as to what the problem is.

If a GFI has power, it should trip and reset.
Without a meter, I would go to the panel and run finger down each row of breakers lightly, it may expose the tripped breaker.
Worse case turn each one off and back on, Wait a munute before switching refrigerator or refrigeration(AC) back on.

I'm confused about your question, it does not explain what you did.

You changed a breaker and now your whole home is without power, is that correct?

Did you switch the Main Service Breaker off before changing the
Breaker? In other words, did you replace the breaker while the panel was live?

If so, you may have created a short in the panel and it resulted in the entire panel being shut down.

First, at the main service panel breaker, switch it all the way off and then back on. Did that reset your panel?

Why did you replace the breaker?

Where is the GFCI device, is it a GFCI breaker or is it a GFCI receptacle?