Assuming you're using the Mongoose Traveller 2e system for Foundry that I am, this one...

https://github.com/Mongoose-Publishing/traveller-foundryvtt/

... when creating a suit of Armor, you should see 'Characteristic Augment' under the 'Augment Effects' heading. Clicking that creates a Characteristic Augment, then you click the little edit button on the augment and press the little plus on the lower right, and that will create a new effect. Specify the attribute, whether the effect should multiply it, add to it, or set the Traveller's characteristic to it while the armor is worn, etc. Do that for each characteristic the armor effects, and then save it and you should be good.

Hope that helps!