I have a dataframe indexed on date with some dates missing (that's ok, they are non-trading data and this is stock data).

How do I access the next row, when I know the previous date, e.g.

```
date  Open
01-01-2021  501
02-01-2021  508
04-01-2021  511
05-01-2021  518

```

I would like a function that, when I input '02-01-2021', it outputs the values for 04-01-2021 (without knowing how many days in between might be missing. I am assuming there may be some iterator, or index number I can access?