Can someone explain why the Hebrew Tannyn is translated as dragons in the KJV but in other bibles is translated as Jackals?

So, don't use the KJV. There's no reason to think it is special in anyway. It was not the first English translation, and it won't be the last.

I recommend either the NKJV, if you think the Textus Receptus is the best Greek Text for the New Testament, or the New American STANDARD Bible (not to be confused with The New American Bible) if you don't. The NKJV is a little easier to read than the NASB.

No one can explain the bibles since they are all fictions

The KJV is so badly translated, unintentionally and intentionally, that it isn't even considered to be a real Bible.

Its Strong's H8577 - tanniyn

That same Hebrew word can mean all these things

dragon, serpent, sea monster

dragon or dinosaur

sea or river monster

serpent, venomous snake

It derives from Strong's H8565 - tan meaning

dragon, maybe the extinct dinosaur the plesiosaurus, whale

In most every language, single words can have multiple meanings

The word "jackal" is not used in the KJV - but Dr Strong says it can also mean "jackal"

tannîyn, tan-neen'; or תַּנִּים tannîym; (Ezekiel 29:3), intensive from the same as H8565; a marine or land monster, i.e. sea-serpent or jackal:—dragon, sea-monster, serpent, whale.

Tanniym appears 28 times in KJV scripture and here is a breakdown of how they translated it

AV — dragon 21, serpent 3, whale 3, sea monster 1

its called OLDE English

the KJV uses english from the 1600's