§1. If the impediment is public, both parties must renew the consent in canonical form, without prejudice to the prescript of can. 1127, §2.
§2. If the impediment cannot be proven, it is sufficient that the party conscious of the impediment renews the consent privately and in secret, provided that the other perseveres in the consent offered; if the impediment is known to both parties, both are to renew the consent.
Source: Code of Canon Law (Vatican.va)