You have to remove the evaporator cover panel, inside at the back of the freezer compartment to get to the evaporator fan. Access is through the front of the freezer compartment
Here’s a link that may help.
Click on the Freezer liner parts diagram. Part #11 is the panel and part #26 is the evaporator fan motor.
If the fan is not operating at all: (remember both doors need to be closed for fan to operate unless you manually operate the door switch of the open door),
Disconnect the fan from the wiring harness and use an Ohmmeter to test the fan motor winding for continuity. Don’t know what the resistance should read but usually they are in the vicinity of 25-100 Ohms and certainly not open circuit. Remember to disconnect the power from the refrigerator when using an Ohmmeter.
If the fan motor winding test OK then reconnect power to the refrigerator and test for voltage at the fan motor harness plug. If there is no voltage on the fan motor, unfortunately there is no wiring diagram but check the control board for the same coloured wires. Although if it is only a two wire fan connection then the black wire will be the neutral wire (L2 in USA parlance) AC connection and will be multipled to other AC powered components e.g. lights etc, so look for the other colour only at the control board. Use the Ohmmeter to verify that there is continuity of the wire from the control board to the fan motor plug as it may go through other connectors and not be a direct link. If the wire tests OK then check if power is on the wire at the control board.
Hopefully a start and apologies if you already know how to use a DMM (digital multimeter) to perform tests safely etc.