How do I open the back of this iron?

Metric

We have removed the only screw we can get to but can't get the handle off to get to the inside screws

You have to take part the iron by unscrewing the three bolts on the side handle with a small phillips driver. Then loose the allen screw on one side of the black thermostat wheel to unloosen it. Then take out the two bolt plastic protectors under the handle and unscrew the two allen bolts, carefully separate the top from the botton of the iron, carefully not to pry loose the cables from the top to the hot shoe.
On the back you will see a small white square box, that is the thermostat, which has a button on top, all you need to do is to push it in. This will make the iron heat up unless you have a thermostat failure (Black wheel with temperature indicators), which you will need to order the part and change it.

Sounds like a 'TORX' head.
Does it look like a 'star' inside the screw head? A six-sided star? If so, then it is a TORX head.
Look carefully at it, and determine whether or not there is a small pin sticking out of the center.

The screw you are trying to remove is either a Flat-Head (-), a Philips (+) or a TORX (*).

You can get TORX bits almost anywhere, from the Hardware store, the Auto-parts store, to a Dollar store. You can get them with, or without, the little hole for the pin in the head.

You will probably want to buy a little 'set' that has multiple sizes of bits, and a driver, with an extension for reaching into those deep holes.

I am not familiar with your particular iron ... however, I am familiar with different types of "bits" I suspect yours are security "Torx". Torx look like a "allen" with points. Some call them "star". A Torx 'security' will be the star shape with a pin in the center, disallowing a regular Torx bit from entering. If you will take your Iron to the Hardware Store or your local Auto Parts store and show to the salesman, I am certain they can sell you the proper bit to remove the cover on your Iron. You may have to purchase a handle at the same time.

There are other types and yours may not be Torx. It could be any of many including a thing that looks like a philips but only three slots instead of 4 or a 'clutch' or it could be a 'one way' or other special bit.. The person at the store should be able to identify the appropriate tool immediately. If not, there are probably more than one store in your town ... go to he next and so on until you get the necessary tool.

Thanks for your question today @ FixYa.com

Probably what they call a torx head. If it has a tip in the center then it will be a security torx head. sets of torx head wrenches or screwdriver type are readily available.

look under the manufacturers stickers normally the screws are well hidden, but at the back of iron underneath there are normally two screws and a third that is in the handle once you remove the backplate

they do take a special tool. However I have used an allen wrench and it will remove them. Take them to a local hardware store or sears and get the same screw thread pitch in stainless steel and with a phillips or slotted head

I got the Torx security bit at Ace hardware for a couple of bucks

Sears sells a screwdriver set (47486 is written on the handle) that has a lot of non-standard drivers. There is one on there that will fit the nuts on this unit.

Also, I used a rubber tube from an Auto parts store to replace the cracked hose. I figured the Automotive hosing was designed to withstand the heat of an engine. So, it should work on this iron.

Bring the cracked iron hose with you to the auto parts store.