I would like to pay unpaid taxes from a previous year, is that possible to do while filing this years taxes or will that have to be separate?

Do you have a refund this year?  They will automatically take anything you owe out of any refunds you get.  You don't have to do anything.  But you should try to pay it as soon as possible to stop the interest from accruing.

You can make payments to the IRS directly by using this IRS website - <a rel="nofollow" target="_blank" href="https://www.irs.gov/payments">https://www.irs.gov/payments</a>