Open document, then go to Tools → Options → LibreOffice → General and check “Enable experimental (unstable) features”. A new option Tools → Macros → Record Macro will show up. Once you click on it macro recording will start, so make sure you only do what you want to be done every time you start that macro later, which is, if I understood correctly, deleting contents of some cells. Select those cells, if you want you can hold and drag the mouse over them in case they are connected or pick individual cells holding
Ctrl and clicking on them one by one. Once you do that press
Delete key to clear them and when you finish click on “Stop Recording” button. A dialog will show asking you to save newly created macro. If you want to use it only in current document, save it under that document’s filename in the list, entering appropriate name for the macro. Now you can start it by going to Tools → Macro → Run Macro.
But there is a way to make it more comfortable for users. Open View → Toolbars → Form Controls, click on “Push Button” in that toolbar and add it to a suitable location in a document. Right-click on that button and select “Control”, open “Events” tab, and click on “…” next to “Execute action”. When “Assign action” dialog appears, make sure “Execute action” is selected, then click on “Macro…” and add the one you recorded. After confirming opened dialogs, click on “Design Mode On/Off” button in the Form Controls Toolbar to exit Design Mode. Now you can do what you wanted by clicking on a newly created Push Button. Save the document.