Which is not another; but there be some that trouble you, and would pervert the gospel of Christ.
which is really no gospel at all. Evidently some people are throwing you into confusion and are trying to pervert the gospel of Christ.
ὃ οὐκ ἔστιν ἄλλο, εἰ μή τινές εἰσιν οἱ ταράσσοντες ὑμᾶς καὶ θέλοντες μεταστρέψαι τὸ εὐαγγέλιον τοῦ Χριστοῦ.
o oyk estin allo, ei mē tines eisin oi tarassontes ymas kai thelontes metastrepsai to eyaggelion toy Christoy.