Breaking "tutajiokoa" down:

tu + ta + ji + okoa,

tu- = first person plural "we",
-ta- = future tense marker, -ji- = object infix. to agree with the class of the object receiving the action. Here, the reflexive -ji- for the m-/mw- noun class of "watu". Please note that "watu" is not explicitly stated but implied,
-okoa = verb root "save"

To check which noun classes take which object infixes, refer to the tips and notes here https://www.duolingo.com/skill/sw/Object-Infixes

Maybe i misinterpret what is stated, but please note that the reflexive "-JI-" does not always imply the "M-/WA-" class as you can see from this example: "Nchi yetu inajitegemea kwa chakula" = our country relies on itself for food.

-okoa (free, rescue, save) I said "We will free ourselves" Survey says? ... Nope