Slide the axle in with the quick-release lever opened. As soon as the axle thread engages with the thread of the opposite side, close it by turning clockwise.

In its end position the quick-release lever should be tight so that it can no longer be turned.

The best closing position is in nearly upright position in front of the lower fork leg. If the lever cannot be closed completely in the correct position (or is too loose), unscrew it, take it out and re-align the axle by pushing down the lever part and turning it against the shaft.