Managers can submit picks for their players, including after the deadline, via the Manager -> Submit Player Picks page, which is located at https://officepoolstop.com/Managers-Only/SubmitPicks.  From here you can select the player, and if pertinent a past week, which will take you to the submit picks page. After the picks are made, the league will reprocess the standings.

On a mobile device, hit the Menu button, click on Manager, then find the 'Submit Player Picks'' page in a pulldown similar to the above image.