You can modify a chart’s data (numbers, dates, or durations) at any time. You can add and remove entire data series, or edit a data series by adding or deleting specific data from it.
Tap a chart, then tap Edit Data.
Do any of the following:
Add a data series: Tap cells, then enter the data comprising your new data series.
Remove a data series: Tap the colored bar for the row or column you want to delete, then tap Delete.
Reorder data series: Drag a colored bar for a row or column to reorder the data series.
Enter dates, times, and durations: Tap 
, turn on Full Keyboard, then enter your data.
Tap Done.
When you add a chart, Pages defines default data series for it. In most cases, if a table is square or if it’s wider than it is tall, the table rows are the default series. Otherwise, the columns are the default series. You can change whether rows or columns are the data series.
Tap a chart, then tap Edit Data.
Tap , then tap Plot Rows as Series or Plot Columns as Series.
Tap Done to return to the chart.
Sharing the x-axis means plotting a single kind of value along the x-axis, while allowing for multiple kinds of values plotted along the y-axis. By default, the x-axis values are shared among multiple sets of y-axis values in some types of charts.
Tap the chart, then tap Edit Data.
Tap , then tap Share X Values.
Tap Done.
If you can’t edit a chart, you may need to unlock it.