👉300sAD: Athanasius quoted 1 John 5:7 on Page 21 of his "Disputatio contra Arium":

Greek: "Πρὸς δὲ τούτοις πᾶσιν Ἰωάννης φάσκει· «Καὶ οἱ τρεῖς τὸ ἕν εἰσιν.»"✅
English translation: "In addition to all these, John affirms, ‘and these three are one.‘"'✅
"Disputatio contra Arium" Document Link (see Page 21)

It is obvious Athanasius, when he was alive in the 300sAD, had Greek manuscripts of Scriptures that contained 1 John 5:7, in order to for him to quote 1 John 5:7's words of "and these three are one."
Athanasius was alive 200-300 years after 1 John was completed, so he & Christians had access to Scriptures that did contain 1 John 5:7, since he quoted 1 John 5:7 in "Disputatio contra Arium". Athanasius is an early Greek witness for 1 John 5:7.
Modern versions (NIV, ESV, NASB, ASV, etc) erroneously remove 1 John 5:7; King James Bible rightly/correctly keeps 1 John 5:7: For there are three that bear record in heaven, the Father, the Word, and the Holy Ghost: and these three are one. ✅

Anti Modern Versions