Go to the Revalidatie Friesland website and scroll down a little until you see: 'Login in E-rehabilitation' sees.

Enter your email address and password and then click 'Login'.

After you op 'Login' Once you click, you will be asked to enter a code.
Depending on how you have set up the Two-Factor Authentication, you will receive the code by email or you will have to retrieve the code in an authentication app.

If you have set up Two Factor Authentication via email, you will now receive an email containing a code.
You can enter this code on the E-Rehabilitation login page. You will then be logged in immediately.

If you have set up Two Factor Authentication via the app, you can now open your Authentication app.
Enter the code stated under E-Rehabilitation on the E-Rehabilitation login page. You can then log in.

NB:
The code in the Authentication app changes every minute.
Make sure you have entered the code on time and otherwise wait until the code has been renewed.