Recently got the Helm of Teleportation:

This helm has 3 charges. While wearing it, you can use an action and expend 1 charge to cast the teleport spell from it. The helm regains 1d3 expended charges daily at dawn.

I can't find anywhere, but what is the range of this teleportation? 30ft? 60ft? unlimited?

The range is given in the Teleport spell.  To whit: there is no maximum range, you can teleport anywhere you like within the same plane of existence, but the less familiar you are with the destination, the higher the chance for something to go wrong.  If it goes wrong enough, it can be a campaign ender.  Nevertheless, the Helm of Teleportation is an extremely powerful item.  Nice find, and be careful with it.

Since the Helm allows you to cast the Teleport spell, you need to look at it:
https://www.dndbeyond.com/spells/teleport

If you look at its description, the limit is:
"The destination you choose must be known to you, and it must be on the same plane of existence as you."

So the range is basically only somewhere on the same plane.

Thanks for the quick answers...

but can you bring a passengers. ¯\_(ツ)_/¯

Again, read the spell the item allows you to cast.  But the answer is yes, up to 8 others