From the data given, to find the take off mass you need only to add the fuel at take off to the MZFM given of 86400 kg.
If the aircraft has 35500 kg of fuel on the blocks and 1000 kgs of fuel is used for taxi. The mass at take off will be 86400 + 34500 = 120900 kgs.
The MZFM is a structural limit that cannot be exceeded. It includes the DOM + Traffic Load. An increase in mass can therefore only be achieved by adding the fuel required !