The A.V. overlooks the article with the participle - the one seeing. Hence Rev., correctly, I John am he that heard and saw.
Had heard and seen (ἤκουσα καὶ ἔβλεψα)
Aorist tense. There is no need of rendering it as a pluperfect. Rev., rightly, I heard and saw. The appeal to hearing and seeing is common to all John's writings. See Joh 1:14; Joh 19:35; Joh 21:14; 1Jo 1:1, 1Jo 1:2; 1Jo 4:14.