Perhaps this will help:
2016 - MX-5 - Transmission/Transaxle (should be similar)
AUTOMATIC TRANSMISSION SHIFT KNOB REMOVAL
1. Engage parking brake.
2. Perform the following procedure to remove the selector lever knob.
a. Shift the selector lever to the N range.
b. Insert the tool (width: 2 mm {0.08 in} or less, thickness: 1 mm {0.04 in} or less) on the rear side, as shown in the figure.
c. Lift the tool horizontally in the direction of arrow (1) shown in the figure and detach the tab, and then remove the lock release button cover in the direction of arrow (2).
d. Remove the spring.
e. Remove the selector lever knob.
2016 - MX-5 - Transmission/Transaxle (should be similar)
AUTOMATIC TRANSMISSION SHIFT KNOB REMOVAL
1. Engage parking brake.
2. Perform the following procedure to remove the selector lever knob.
a. Shift the selector lever to the N range.
b. Insert the tool (width: 2 mm {0.08 in} or less, thickness: 1 mm {0.04 in} or less) on the rear side, as shown in the figure.
c. Lift the tool horizontally in the direction of arrow (1) shown in the figure and detach the tab, and then remove the lock release button cover in the direction of arrow (2).
d. Remove the spring.
e. Remove the selector lever knob.
