Why is the findIndex method showing second occurance too?

Basically the idea is that my code chooses a random element from an array. That element is the arr[i].answer and is placed at the end of that array. Then i want to make the first occurrence of that answer as an *. I used the findIndex method as i thought that the first occurrence of my answer will become the * however both first occurrence and the last element have become an asterix.

Here is the code

arr.forEach(element => {
              arr[i].answer = arr[i].sequence[rndElement];
              arr[i].sequence[arr[i].sequence.length - 1] = arr[i].answer;

              function isFirst(element, index, array) {
                return element === arr[i].answer;
                }

                let index = arr[i].sequence.findIndex(isFirst);
                arr[i].sequence[index] = "*";

              
          });

Above is the necessary code, below is all the code for reference

const arr = [];
    const input = document.getElementById('answer').value;
    const rndElement = Math.floor(Math.random() * 6);


    function displaySeq() {
        var i = 0;
        while (arr.length < 21) {
            const rndInt = Math.floor(Math.random() * 50);
            const iterator = Math.floor(Math.random() * (8 - 3 + 1)) + 3;
          arr[i] = {
              sequence: [rndInt],
              answer: 7,
              guess: []
          };

          let j = iterator;
          while (arr[i].sequence.length < 7) {
              arr[i].sequence.push(rndInt + j);
              j+=iterator;
          }

        arr.forEach(element => {
              arr[i].answer = arr[i].sequence[rndElement];
              arr[i].sequence[arr[i].sequence.length - 1] = arr[i].answer;

              function isFirst(element, index, array) {
                return element === arr[i].answer;
                }

                let index = arr[i].sequence.findIndex(isFirst);
                arr[i].sequence[index] = "*";

              
          });
          i++;

       }  
        console.log(arr);
    }