-Place Hi-Low in Neutral
-Remove four bolts with 1/2" wrench.
-Use wrench or screwdriver to neutralize shifter untill they are side-by-side. -Align shifter bottom levers to best fit dimple for hi-low and slot for shifter.
-move shifter base and levers until bolt holes align and place bolts and holes and start threads. -Tighten one bolt snugly then all tight.
FROM NOW ON - use PERFECT "H" pattern shifts and it won't happen again.
keep a 1/2" box end wrench on tractor and repeat above steps with each shifting accident.
If you feel confident, do the temp fix in the URL below. The only true fix is new bearings, mostly on the bottom shaft or a complete transmission rebuild. Water in the Gear Oil is the often culprit for premature bearing wear. Change fluid.
Wayne in VA