4 Heb “If you [= you must, see the translator’s note on the word “do” later in this verse] swear/take an oath, ‘As the Lord lives,’ in truth, justice, and righteousness …”
5 4:1–2a consists of a number of “if” clauses, two of which are formally introduced by the Hebrew particle אִם (’im) while the others are introduced by the conjunction “and,” followed by a conjunction (“and” = “then”) with a perfect in 4:2b which introduces the consequence. The translation “You must.… If you do,” was chosen to avoid a long and complicated sentence.
6 Heb “bless themselves in him and make their boasts in him.”

In other versions

ESVEnglish Standard Version

and if you swear, ‘As the Lord lives,’

in truth, in justice, and in righteousness,

then nations shall bless themselves in him,

and in him shall they glory.”

NIVNew International Version (2011)

and if in a truthful, just and righteous way

you swear, ‘As surely as the Lord lives,’

then the nations will invoke blessings by him

and in him they will boast.”

CSBChristian Standard Bible

then you can swear, “As the Lord lives,”

in truth, justice, and righteousness,

and then the nations will be blessed by him

and will boast in him.

NLTNew Living Translation

Then when you swear by my name, saying,

‘As surely as the Lord lives,’

you could do so

with truth, justice, and righteousness.

Then you would be a blessing to the nations of the world,

and all people would come and praise my name.”

LEBThe Lexham English Bible

and you swear, ‘As Yahweh lives,’

in truth, in justice, and in righteousness,

then nations will be blessed by him,

and in him they will boast.”

KJV 1900King James Version

And thou shalt swear, The Lord liveth, in truth, in judgment, and in righteousness; and the nations shall bless themselves in him, and in him shall they glory.

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