How to store a value to a variable when a user reacts to a message?

I have figured out how to do make a bot react with its message from the following code:

if(message.content === "!start"){
        message.channel.send(serve).then(message => {
            message.react('764193096060764211');
        })
}

(serve is an embed stored in a variable)

I want the user to react with it and the bot to do something with that information, for an example, storing the value 1 to a variable called startingServe. If the user doesn't react within 5 seconds, I want the bot to message "Gamer Ended". How do I do this? Looking forward for the help from this community! If there's anything else needed from me to answer this question, it is fine to ask.