Is there a reason to undo entries with a special button.
Excel already has an Undo function, and there is the option to undo a series of actions.
Do you need more than this, and if so how is the initial state determined.
If data is entered, then there is a pause and more data is entered, how far do you go back - to the state before the second lot of data entry or to the state before the first lot of data entry, or ....where/when
Do you want to re-load the worksheet, and if so will you need to stop everyone from saving any changes.
Let us have more information to help offer a possible solution.