Previous posts about this the dev has given the answer to you'll have to type in iron key and look at other people's post to find it I had this same issue til I begun exploring the discussions

Originally posted by K Wha?:

I have gone into the mine so many times. Went down the elevator but I cant find the lever, they won’t drop it for me so i can open the gate

Hey, have you found them?
They are a little hidden and easy to walk by.
I can spoil their location for you if you want it.

I found the lever it was straight in front of me on the ground as you enter the room where the gate is closed. It was never there before.