OK, here's what you need to do...
First, remove all 3 setscrews from the knob and set them aside. Degrease one of them as it will be getting loctite.
Next, it looks like the lower detent clicker pin in the scope body has rotated 90 degrees, and that's what is probably keeping you from sliding the turret all the way back down. Those detent pins are at the 6 o'clock position on the turret housing facing the eyepiece. Rotate the lower detent pin so the notch is vertical like the upper pin.
Now, pull the locking collar on the elevation knob up so it covers the setscrew holes. Slide the knob back on the turret and make sure it's seated all the way down. Probably have the 7 mil mark or so facing the alignment notch on the scope body when you install the knob so the second rotation indicator mechanism or zero stop won't get hung up on the pin that actuates them At this point, while keeping light finger pressure down on the center of the knob, rotate it to make sure you have the zero stop, 0.1 mil clicks, 1.0 mil MTC clicks, and that the second rev indicator popup works.
Next, while maintaining downward pressure on the center of the knob, push the locking collar down into the "locked" position to get access to the setscrew holes. Use a flashlight and look into one of the setscrew holes, the setscrew holes should line up with that groove on top of the elevation turret spindle in the scope body. If the setscrew holes are above that groove, the knob is still sitting too high and you may have disturbed/rotated one of the detent clicker pins when sliding the knob on.
After you've verified the set screw holes are aligned with the groove in the elevation turret spindle, with the locking collar still in the down/locked position and while keeping light finger pressure downwards on the center of the knob, apply some medium strength loctite to one of the setscrews and install it in the knob. NOTE: S&B wants the 2 "unplugged" set screws that get used for zeroing clocked 90 degrees apart, so make sure the "plugged" setscrew you just installed isn't in the middle hole of the hole pattern. Putting the "plugged" / loctited set screw in the location closest to the objective with the turret dialed to zero is S&B's standard spot.
Run that loctited setscrew down until you just feel it touch the elevation turret spindle, then loosen it about 1/4 turn. This is the "plugged" setscrew that gets the plastic plug, and the only function it serves is to poke partway into that groove on the elevation turret spindle so you can't pull the knob off when you loosen the other 2 setscrews to zero the turret. If this setscrew is too tight it will rotate the elevation turret spindle and you can't zero the scope, but you also don't want it so loose it doesn't capture the groove on the spindle and allows you to pull the knob off the turret. A good check to do here is to look through the scope while dialing the elevation turret. It's going to click, but the reticle should not move. If the reticle moves, that setscrew is contacting the elevation spindle and adjusting the turret, so back it out a little more before the loctite sets.
After the loctite on the "plugged" knob retention setscrew has set, stick the plastic plug back in it, then reinstall the two other setscrews that are used for zeroing the turret... you should be back in business.