Usually you can create a bunch of affirmations and then copy them to a text to speech software. After downloading that audio you can then put it on an audio editing software like audacity for example. You can then speed up the affirmations and also make it quieter so it can go past your conscious threshold and then enter the subconscious.
Subliminal message results are temporary and they have to be listened daily to maintain the results. If you are looking for results that has to be permanent you are better off doing magick. It is superior to subliminals in most scenarios and unlike subliminals that work mostly with the programming of the subconscious, magick can affect the external environment more effectively.