On Appraisd, you have to be invited to give feedback. The invitations are sent through Appraisd by the person managing the appraisee.
If you've been nominated to give feedback, you'll receive an email and the invitation will show up on your Appraisd dashboard:
Click the X requests for feedback button on the far right to proceed.
Click Give feedback now for the relevant person:
Once you've completed your feedback, you cannot change it unless you are re-invited to give feedback.
If you need to make changes, ask the manager or an Administrator to re-invite you from the appraisee's profile page.