To fill in questionnaires that a coach/researcher sent you, first go to your Home page.
From there, click on the Questionnaires button on your left. This button will have a red dot in case you have questionnaires yet to fill.
You will be presented with a menu with several sections. The top section, called Fill out questionnaires, shows the questionnaires you can fill in.
Can you not see this menu? Then try enabling questionnaires.