If you decide to work past age 65 and have an employer-sponsored healthcare plan, you can model delaying Medicare.
Step 1: Go to My Plan > Expenses
Step 2: Open the Medicare Expenses (65 through longevity) section
Step 3: Enable the Estimator (if not already enabled)
Step 4: Press ✎ (pencil) to edit your Medicare selection
Step 5: Press on "Add employer sponsored Medicare coverage +"
Step 6: Enter your annual out-of-pocket costs and the age these costs will end
Step 7: Press Next
Step 8: Make sure to press Save