The tool will never automatically withdraw funds from a 529 account. You must either set up manual one-time disbursements or annual disbursements per account. The basic steps are below:
Step 1: Go to My Plan > Expenses
Step 2: Open the Disbursements section
Step 3: Press "Add a Disbursement +"
Step 4: Indicate the amount in future dollars and whether or not it is recurring (for this exercise, it will be a one-time disbursement). If you plan to pay over a period of time select "annual."
Step 5: Select that it will be coming from your 529
Step 6: Enter the age the primary planner will be when you expect the disbursement to occur. If a recurring disbursement, set a start and end age
Step 7: Decide if this disbursement is qualified (tax-deductible) or not. Withdrawals from 529 plans are tax deductible by default.
Step 8: Don't forget to press "Save" when complete