grammar - What is the meaning of ことに当たるように?

What is the meaning of ことに当たるように in this example (there is already a post of にあたって/にあたり, but I can't understand)?

以後{いご}はトムと協力{きょうりょく}してことに当{あ}たるように。

Answer

It's a fixed phrase:

事に当たる

１ 物事を担当する。従事する。「式典には全社をあげて―・った」
(Translation: take charge of / engage in some work: "The whole company was involved in the ceremony.")

^{(The linked entry also has a second definition, but it's classical usage. Forget it.)}

ように that ends a sentence should be interpreted as formal command.

From now on, you should cooperate with Tom to handle it.

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You may be confused because both こと(①-3) and 当たる(5-㋐) are used here in their original meanings, rather than as function words. The best practice is writing this こと in other than hiragana, but sometimes they do this way. Nevertheless, you'll know the こと isn't a nominalizer but a standalone noun because 協力して can't connect to it in this form.