The foot pedal on my Kenmore 116-31912100 stays in down position like a spring is broken.

Most vacuums have plastic tabs and a plastic mechanism of some sort to that will engage those tabs to make it stay upright.
I am suggesting either the tabs are worn down, or are broken off, or maybe the locking mechanism is broken.
These parts are most often not replaceable, unless you can find an identical machine with these still good on it, and swap whatever parts are necessary to fix it.
Machine is a "throwaway " model.
When it breaks, you are expected to buy a new one.
God bless your efforts.

Remove the assembly that holds the foot pedal by removing the three screws after you've removed the bottom plate and brush roll. This allows you to get the nozzle housing out of the way so you can rotate the assembly holding the foot pedal from the metal pivot. Remove the e clips from the shaft and pull the shaft out of the foot pedal (be sure to look closely at the spring and how the shaft are positioned so you can be sure to install them exactly the same way you took them off. It is not a hard job but can be confusing the first time. It's not an expensive fix to have done by your Riccar dealer.

It's not hard to do but is almost impossible to explain how to do it. If you can look at one already installed on the shaft holding the pedal you can see how it's done. Visit your local Riccar dealer.

here is a video how to repair the pedal

Hi,

to find that repair manual that you've requested and fix your vacuum so it can move into upright position, you can ask Miele to email you the manual by calling them at 888-996-4353

Thank you.

if you open the left end of the machine .. look inside above the needle and to the back .. you will see a pivot bolt that has either come loose, broken off or fallen out .. replacing that bolt should fix the problem ..

I had same problem - the foot release pedal would not spring into place when unit was upright (but would work if you nudged in place with your foot). I installed a replacement part, and it didn't fix the problem. I cut out a small sqare of sponge and jammed it behind the flat end of the bent plastic spring on the release pedal, and it now springs back as it shoud. Hope this helps.

• The motor / cord compartment cover must be removed to access the cord reel. There are four screws that hold the cover to the chassis. Two of the screws are found under the cord-retractor-foot-pedal on the top back of the canister. To access these screws the pedal must be removed. To do this, press the pedal down and look (from the top) for the four plastic clips that attach/hold the pedal hinges to the cover. There are two at the end corners and two in the middle. Using a long, thin flat-head screw driver (or similar instrument) press each clip to unhook/popout the hinges. Note: the foot pedal spring will also come out when the pedal is removed.
  
  The other two screws are found under the curved hinges of the vaccum bag compartment cover. To access these, lift the cover as if accessing the vacuum bag. Keep pulling the cover back until the hinges release from the motor cover. Don't worry, it is disigned to do this and will not break but it may require a little force. A long phillip-head screw driver will be needed to access and remove each screw

There is no release, the part is a plastic handle release lever, you can find those at www.hesco.com, the cost is approximately 2.29 each, I have replaced more than 20 of these on the commercial vacuums for my cleaning crew, the part is easily broken and easily replaced. I always have 6 or more on hand.
Turn the vacuum over, remove the bottom plate, with a flat head screw driver punch out the old part. turn the vacuum upright again after the broken part is removed. With the body laying back on a hard surface, carefully push in the new part. Unfortunately, these are plastic, too bad they cannot design a more sturdy part for this.

You will have to take the top loose so you can put the handle release in its place. It probably isn't in the right place, either that or a piece of it broke off and it needs to be replaced.