Very simple: Holy Tradition records something Christ did, which is not recorded in the Gospels, to wit, miraculously creating an image of his face by pressing a cloth to his face, and sending it to King Abgar of Edessa, who had faith that merely seeing the Savior would cure his leporsy.
Now 'sola scriptura' types will insist this never took place because it is not in the Bible, in plain contradiction to St. John's conclusion, which say Christ did many things not recorded there in (and so many that you can't claim he is referring only to what is recorded in the Synoptic Gospels, but omitted in John's, since that would not amount to enough books the world could not contain them.)
Either there are not enough deeds of Christ not recorded in the Scriptures so that (on the Holy Apostle and Evangelist John's estimate) the world could not contain the books recording them, and we have a false passage in Scripture, or the Scriptures are not complete, as is necessary for the 'sola scriptura' position.
So when assessing what things "Jesus did" you are including things that He didn't do directly?