How can I start it?

You can't. The security system and immobilizer is there to stop EXACTLY what you are trying to do, start the car without the key and security code credentials.

Your local dealership with make you a key based on the VIN Number. Then you have to reset the security system.

Or you can try a local mobile locksmith.

Or find the key. If you lost the key in the snow, look up 'Ring Finders', a global network of metal detectorists that find lost rings and keys.

lost all our keys,? what is the key story, there sure is one.
no year car told, wow.
E32 model 1986?or (no)
Sixth generation (G11/G12; 2015)???? IMMO does not allow, you to lose all keys, then buy one and start the car, in fact that it is A#1 PURPOSE. to prevent that.

1st google hit, read

https://www.bmwcodingdatabase.com/interesting-about-bmw/readers-ask-lost-bmw-keys-what-to-do.html

Your keys have chips in them, there is no bypass, you'll have to get at least 1 key programmed.

probably not your key that you lost has a chip in it go to a locksmith he might be able to duplicate the chip for you for a lot less money than the dealership

You may have to go thru key reprogramming steps. Programing New Key on Jeep Liberty

Best you see a lock smith.

you must go to dealer and have akey made because the one you lost probably has a theft deterant by pass built into key thats why it wont start you have a computer chip in your original key that by passed alalrm and it would start ur car they will need ur vin number

the key has lost it's code, there is a chip in the key that communicates with the security system that the correct key is in the ignition and that the vehicle is allowed to start.

if you have any other keys on your key ring remove these and try again.
if no start and light still flashes the computer will need reprogrammed to accept the key.
the dealer can do this in like 10 -15 minutes usually.

to disarm the alarm. turn the key in the door or trunk.

lost my key and have to take it to the dealer case of a code on the key. a week later found my old keys, made me mad cause they are not cheap. good luck