Android:
Go to the link provided by email or on intranet to download the app.
Log in with your own credentials
IOS:
Step 1:
Go to the link provided by email or on intranet to download the app.
Log in once with Password: Declaree
Press Install.
The app will now download.
Step 2:
Now the app will need to be trusted, go to Settings > General > Profiles or Device Management.
Click on Declaree B.V. under Enterprise Apps and then Trust 'Declaree B.V.'
You can find more information here: https://support.apple.com/en-gb/HT204460
And after this you can log in with your own credentials