During upload – at least on the website (not sure about mobile apps) – you can add observation fields. If you look at the left side of the screen, you’ll notice there are Details, Tags, Projects, and Fields. You can select fields, and add a field that you want to use, and then you can assign a value to that field. If you want to add the same field with the same value to multiple observations, just highlight the multiple observations before you add the field value.
If you want to add values after upload, on the website, hover over your account icon on the upper-right corner of the screen. That should show a drop-down menu where “Edit Observations” is the second item in the list. Click on that. That should bring you to a “Your Observations” page that has an “Add Observations” button, a “Batch Edit” button, and a “Search” option. If you want to filter for specific observations first, use the “Search” thing. Then click the “Batch Edit” button. From there, you should be able to add fields to selected observations. I think the format of the Batch Edit screen does sort of look like the table you’re asking for.
If you’re trying to add fields to observations that are not yours, then I think you have to do that one observation at a time, and that’s only possible if the observer lets you. But depending on what you’re trying to accomplish, you might be able to add other people’s observations to your own custom project – again, if they let you. Or if you’re just trying to flag model observations, you could mark those observations as favorites.
I’m not sure if this is exactly what you’re looking for, but I hope this helps.