This transactions is not to appear on Form 8606. Form 8606 Part II only applies to Roth conversions from traditional IRAs. A 401(k) is not an IRA. ( @user17708643219 , this distribution was not from a traditional IRA.)
With regard to tracking Roth IRA basis:
While Form 8606 does report Roth conversions from traditional IRAs, it is not useful in tracking your Roth IRA conversion basis over the years. Conversion tracking is your own responsibility. TurboTax does help you with that by keeping track of your basis on TurboTax's IRA Information Worksheet. TurboTax will use that Information whenever it becomes necessary for TurboTax to prepare Form 8606 Part III.
The IRS does not track your basis. If the IRS ever suspects that you have misapplied basis on Part III of Form 8606 or that you have treated a distribution as a qualified distribution that they believe is nonqualified, they will ask you to provide records that support your position. With regard to the tax code, you are essentially treated as guilty until proven innocent by the documentation that you provide in response. Supporting documentation would generally need to be records of the individual transactions, not summaries of transactions. (The information on Part III of a Form 8606 already reflects a summary of the transactions, so if the IRS is already questioning that, a summary is not enough.)