You can open “personal items”, there you see each and every station where you have any items in store. Rightclick on the one you find your module in and set course.
If you don’t find the item in your inventory, I have 3 ideas:
You may be in the wrong station (same station name as in personal items?)
you applied filters (stated in the window: x filtered?)
you did’t buy it properly/immediately (transaction in wallet?).