Quicken will add adjusting transactions to your 401(k) transaction list to identify how much of your contributions came from your own contributions as an employee and how much came from your employer's matching contributions. This is a one-time process, performed during your first 401(k) download.
Quicken automates this process for you by putting placeholder entries in your 401(k) transaction list. Unlike placeholder entries in other investment account types, you don't need to resolve the placeholder entries. Just leave them there—Quicken tracks everything for you.