Learn French: Pour la désamorcer, tire doucement sur le détonateur. - To defuse it, gently pull on the detonator.

In French, object pronouns like la (meaning 'it', referring here to a feminine noun like la bombe) are placed directly before the infinitive verb they belong to.

Doesn't tirer sur usually mean 'to shoot at'?

It can! Tirer sur means 'to shoot at' a target, but it is also the standard way to say 'to pull on' a specific part of an object (like pulling on a string, a lever, or a detonator). If you were just pulling a whole object towards you, like a door, you would use tirer without sur (tire la porte).

Since this is an instruction to a single person, why doesn't tire have an 's' at the end?

In the imperative mood (used for commands), regular -er verbs drop the final 's' in the tu form. So, tu tires becomes the command tire.

How could we use this lesson's focus, une fois que, to say 'Once you have defused it, you will be safe'?