What if I forgot to bring my poster to the conference?
Print it locally.

Hopefully, your conference is in a city of some non-negligible size and not in the middle of nowhere.  Find a copy shop in the city and print your poster there.

Large conferences may even have their own on-site printing, although a last-minute print job may be expensive or even unavailable.

Some people do this in any case, so that they don't have to travel with a poster.

(Your university/employer may or may not be willing to pay for a 2nd printing of the poster)