Nowhere near enough info to go on - top slicing calculation can only be done after the end of the tax year when your total earnings / tax for this year are known. Your level of earnings and tax between now and the end of the year will affect the calculation.
To do the calculation one also needs to know your earnings & tax details for the previous 3 tax years.
It's not rocket science - either pay someone a couple of hundred to do it, or else trust either yourself or a Revenue employee to do the calculation. Either way, it's a calculation that can't be done this side of Christmas.