Hi Allison,
We have a functionality for Local Phenology Programs, called Data Entry Technician, that allows you to do just this! Any administrator can assign any LPP member to be a Data Entry Technician.
First, go to your Manager Users page (linked from the bottom left of your Observation Deck if you are an administrator for an LPP), then select your name and check the box next to Data Entry Technician. Then you can go to the Enter Observation Data page (linked from the bottom right of your Observation Deck) where you'll see a dropdown of your observer emails. You can pick the person whose data you want to edit then make any updates and click the Submit button.
Let me know if you have any questions!