If you try to do a job that exceeds your abilities, you can't deal with it.
Anyone who is in a job that is beyond their capabilities can't cope with it.
上回る = to exceed, to be more than, to go beyond, to surpass
to be in a job = ある仕事をする
能力 = ability/abilities, capability/capabilities, competence
対応が出来ない = can't handle it, can deal with it, can't cope with it
「自分の能力を上回る仕事が来たら対応が出来ない」という表現を英訳すると 「I can't perform a task that exceeds my ability」または「I can't perform a job that exceeds my ability」になります。「仕事」という言葉は「task」または「job」という言葉になります。また、「上回る」は 「exceed」になって、「能力」は「ability」になります。
アメリカ合衆国 
