We don’t know what phone you have. We don’t know what you are running on your phone. We don’t know who your carrier or service provider is. We can’t even be sure what you mean by “sign out”. There might be a million possible “sign outs” that might be done. In short, there is no useful way to answer without a lot more information.
And depending on what you mean by “sign out”, the answer might be “You don’t.” It’s possible that what you’re asking about is disconnecting from a call or from internet usage or a couple other possibilities.
Please provide enough information so we can make guesses.