Trying to add string starting from the right going to the left in a specific area

I’ve been trying to figure out how to add period as a string in a certain place, here’s the code

function fixBalance(amount){
  if(amount <= 99999999){
    var amt = "0." + amount.toString().padStart(8, "0");
    return Number(amt);
  } else {
    return false;
  }
}

console.log(fixBalance(1));
console.log(fixBalance(1000));
console.log(fixBalance(10000000));
console.log(fixBalance(1000000000));

Basically, there are 8 spaces to the right of the 0

After it passes 8 numbers, I want numbers to keep going past the period

For example:

1 = 0.00000001

1000 = 0.00001000 or 0.00001

10000000 = 0.10000000 or 0.1

1000000000 = 10.00000000 or 10

If I were to put in 1000000000, it should be 10.00000000 or 10 as a numerical number

Trying to figure out how to do that with the else statement

Thank you!