If you have received an invitation to complete an ESPD form, this is because another vendor needs your response to the ESPD form to send the bid.
In the message you received through Mercell you will find a link. Follow the link to get to the current tender.
You can also find the tender under the tender search function on the front page of Mercell.
Click Manage Invitations
Click Accept Invitation and click OK in the box that appears
Click through the answer and click on Send answer.