Each test kit contains a "Retourbox", for example:

The Retourbox has the correct address of the lab printed on it and postage is already paid. Just put the the sealbag with your sample in it, close the Retourbox with the "Seal to close" sticker and take your Retourbox to a post office (preferred) or the nearest yellow mailbox.

If you have multiple test kits, e.g. a Basics STD test and a Premium STD test, make sure to send in each sample in its "own" Retourbox, as they are analyzed in different locations of our partner lab MEDISYN SA. Refer to the overview in case of doubt.