Redox, titration, iodometry help!

[twomblyhero]

We completed a redox titration of Iodine
(formed from 1M Potassium Iodide (KI), 0.1M Potassium Iodate (KIO₃) and excess Hydrochloric acid (KCl)


against Sodium thiosufate (Nas₂O₃)

It took 25.8cm³ of 0.1 M Nas₂O₃ to get rid of the formed Iodine.

The question asks:

Use the equation below to calculate the amount of iodide ions that reacts with each mole of iodate ions in aqueous solution

2S₂O₃^2- (aq)+ I₂ (aq) 2I- (aq) + S₄O₆^2-(aq)

and determine the concentration of iodide ions in moldm^-3

I am not sure what this is asking me! Do I need to calculate how the Iodine is originally formed?
I am really stuck on this one! Please help.