First of all, you need a TWINT business customer account. If you don't have one yet, please create an account here.
Do you have an account? Great, then you can start with the configuration!
Log in to the TWINT Dashboard: https://portal.twint.ch/partner/gui/?login
Choose that you want to integrate TWINT in an online store.
Enter all necessary information and click continue.
Select "PSP (Payment Service Provider)" and then - important! - "TFTW GmbH". Fill in the rest of the info and click next.
Check all your entries and then click on "Submit order".
Now you can add your store in your TFTW Account and install TWINT directly from there.