If you need to make changes to your poster letters of presentation after they have been distributed, you can easily do that.
Head to the posters on your event summary.
Click on the poster which requires details to be changed
Delete the letter that was previously awarded
To be able to award a new letter associated with the author you will have to first delete the letter that was previously awarded (the one(s) that contains information which requires updating). To do that, scroll to the bottom of the poster details page and you will see the certificates that have been awarded previously. Click the three dots and then click delete certificate. If you require an update to all the authors' certificates delete all the certificates.
Make the changes you need on the poster
Click the pencil to make changes to the poster details
Edit the fields which require an update.
When finished making changes click "update poster"
Regenerate the letter/certificate
Now you can regenerate the letter/certificate with the updated information. Just hit "award certificates" at the bottom and the certificate will be regenerated with the updated information for those authors for which you had deleted a certificate.