You don't. The tax withholding in box 4 on the 1099-R is applied to taxes paid on the 1040 form line 25. 401(k) distributions are taxed as ordinary income. The default mandatory withholding on a 401(k) is 20% so I do not understand why only 10% was withheld.
However, if you are under the age of 59 1/2 there is an additional 10% early distribution penalty and if you are in the 20% tax bracket then you probably should have had 30% withheld or you will owe additional tax.
**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.**
