Where should I put this loop?

let yourAnswer; // Initialize the variable.

do {
  // Prompt the user for a number and assign it to the yourAnswer variable.
  yourAnswer = prompt('Please type a number!');
} while (isNaN(yourAnswer)); // Continue prompting the user while yourAnswer is not a number.*

*Something like isNaN('123') will return false, so you don't have to parse the yourAnswer variable into a number in the do-while loop. You can do it after the loop.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/isNaN

You have a few things that need to be changed. First, if you're going to be asking for the answer and converting it, you don't want those variables to be constants. You left out the backticks in your alert where you display the randomnumber. Your alert with the randomnumber is a little odd grammatically, as most people would expect the lower number to be first. As for the loop, you would want to use a while loop. Here is a version that should do what you want:

  let yourAnswer = prompt('Please type a number!');
  let yourNumber = parseInt(yourAnswer);

  while (!yourNumber){
    alert(`You need to provide a number. Try again!`);
    yourAnswer = prompt('Please type a number!');
    yourNumber = parseInt(yourAnswer);
  }
  const randomNumber = Math.floor( Math.random() * yourNumber) + 1;

  alert(`${randomNumber} is a random number between 1 and ${yourNumber}!`);