To undo your last action or last few actions, press CTRL+Z.
Click on get data option on the top left and you'll get a drop down menu, Select the type of data you'll be using. In my case I chose Excel.
![](https://docs.microsoft.com/en-us/power-bi/media/desktop-common-query-tasks/commonquerytasks_getdata.png)
Once you've selected the data you can edit before you load it onto power BI. Its always a good practice to edit the data make the report only for required/filtered data.
![](https://docs.microsoft.com/en-us/power-bi/media/desktop-common-query-tasks/commonquerytasks_navigator.png)