Hi Jose Luis,
You can access the URL specific to a candidate invitation to a test in two different ways:
1- Participant Page- Assessments
In the invitation for the test you want to share you will find an arrow in the top-right corner, that is the disconnected mode function, you can copy the link to the test invitation for this participant and paste it into a personalized email.
2- Go to the function Assessment-Assessment Manager. Search for the participant and test you are interested in share the link invitation. Click the arrow in the top right corner of that participant and test invitation to obtain the URL code.