Pending invitations displays your list of responders that have not yet confirmed or approved the relationship.
The Pending invitations tab lets you see all invitations that you have sent to other relations.
You can drop any invitation by clicking on the icon on the right hand side when you mouseover the members row.
Click on the row with the responders name, you will see data related to their status (forms shared with them etc).
You will see a button displaying Resend Invitation email now, press this and they will be sent the email invitation email again.
The responder should then login to NestForms and confirm your invitation. If they do not remember their password, they can use the forgot password feature.