There is nothing to "fix". "Withholding" is money that you earn that is kept back "withheld" that you do not get in your pocket. It is sent to the IRS instead, as an "advance" to pay your estimated tax.
If not enough was withheld, then you received that money in your paycheck and in your pocket instead of being sent to the government - now you have to give it back - same money, you did not loose anything.
Ideally, at years end you neither owe additional tax or receive a refund, which means you neither paid too much or too little in tax during the year.
A large refund means that you gave the government too much during the year (a interest free loan to the government) and now they have to pay it back.
**Disclaimer: This post is for discussion purposes only and is NOT tax advice. The author takes no responsibility for the accuracy of any information in this post.**
