Question: how to make ik fk switch?
Answer: Select the IK handle of the IK chain that you want to animate with FK.
In the IK Solver Attributes, drag the Ik Blend slider to 0.000. ... 
Select Animate > IK/FK Keys > Set IK/FK Key. ... 
Deselect the IK handle.
Select a joint in the IK chain, drag the current time indicator along the Time Slider and rotate the joint.