21 Grk “that one.” The context makes it clear that this is a reference to Jesus, because the reader is told “he was revealed in order that he might take away sins.” The connection with Jesus as the Lamb of God who takes away the sin of the world in John 1:29 provides additional confirmation that the previous use of ἐκεῖνος (ekeinos) in 3:3b should also be understood as a reference to Jesus, as 2:6 was. In Johannine thought it is Jesus, the Lamb of God, who takes away the sin of the world (John 1:29).
22 The ἵνα (hina) clause gives the purpose of Jesus’ self-revelation as he manifested himself to the disciples and to the world during his earthly life and ministry: It was “to take away sins.”

In other versions

You know that he appeared in order to take away sins, and in him there is no sin.

But you know that he appeared so that he might take away our sins. And in him is no sin.

You know that he was revealed so that he might take away sins, and there is no sin in him.

And you know that Jesus came to take away our sins, and there is no sin in him.

And you know that that one was revealed in order that he might take away sins, and in him there is no sin.

And ye know that he was manifested to take away our sins; and in him is no sin.

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