Add values from a current cost column to a cost to date column at the push of a button

I have a budgeting spreadsheet and need to have a point where I magrate
costs from the current period to a costs to date column.

So in column L, I have all my current costs - when push a button I
would like to add those costs to the K column which contains costs to
date.

I was hoping to use a control button of sorts - please help.

Thanks
Peter