How do I file a second w2 that i recieved from my employer if I filed for my first one already ?

It depends.

If you have already filed your tax return, you will need to wait for it to be accepted and then may need to file an amended return.

If you have not filed your tax return yet, you can simply add the new W-2 Form in the Federal section of the program.

1. Select Income & Expenses
2. Select Job (W-2)
3. Click Edit/Add to the right of the Job (W-2) 
4. The next page will have boxes that say "Add a W-2 for..."Select the appropriate taxpayer and enter the information for each W-2. 

Also, if it is a corrected W-2 and you have not filed your tax return yet, you can simply select Edit to the right of your existing W-2, and update your information.  

Be sure to select it is a corrected W-2 as you proceed through the questions.