You are using an IIFE in your for-loop to which you pass the index.
That looks like it was designed to prevent modification of i!

When you do

i = i - 1

at the end of your function, it has absolutely no effect as it only affects the i inside your function.

Here's a good article about variable scopes in JavaScript.

But if you still want to modify i, then one option would be to simply have it be returned by the anonymous function and assigned to the external i variable:

.then (function(fn){

    for (i = 1;i < rowCount + 1; i++){

        i = (function(i){

            var element = driver.findElement(webdriver.By.xpath(//div[@class='table-container'][+i+]/div/strong/a));

            element.getText().then(function(Type){

                var typefromArray = String(Arr[j].split(':')[0]);

                if (Type == typefromArray){

                    // Do something

                    j = j + 1;

                } else {

                    // Do something

                    i = i - 1 // My problem looks to be here, but may be in the transfer of this back up to the beginning of the loop       

                    j = j + 1;

                }

            });

            return i;

        })(i);

    };

That is the solution to the question you asked.

But I'm pretty sure there will be other problems in your code, as you are using a synchronous loop, yet updating the counter in an asynchronously-called function (the function passed to element.getText().then).

I'd suggest you either study a bit about how to handle asynchronous code in JavaScript (you're using Promises right now) or open a more general question about the bigger problem you are trying to solve as there will be some more design hurdles to overcome.

Here's an example of the kind of patterns you may have to use to handle multiple Promises (not meant to be copy-pasted, used ES2015 for brevity):

.then(function(fn) {

  Promise.all(

    Array(rowCount).fill(true).map((_, i) => i + 1) // => [1..rowCount]

      .map(i => {

        const element = driver.findElement(webdriver.By.xpath(//div[@class='table-container'][+i+]/div/strong/a));

        return element.getText();

      })

  // Here we have an array of Promises that we pass to Promise.all

  //   so we can wait until all promises are resolved before executing

  //   the following .then

  ).then(types => types.filter(type => type === typefromArray)

                       .map(type => { /* doSomething */ });

});