Assuming that the 401(k) contained both before-tax money and after-tax money, and the before-tax money was rolled into Traditional IRA and the after-tax money into a Roth IRA then that becomes your "basis" in the Roth that can be withdrawn at any time both tax and penalty free. Any earnings distributed would be subject to tax and penalty.
When you enter the 1099-R for the distribution answer the follow-up questions that your prior contributions was the amount of after-tax money that was rolled over to establish the basis.
**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.**
