You can use JSONata in the property field.
e.g.
[{"id":"c828b9168a3f213f","type":"inject","z":"da8a6ef0b3c9a5c8","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"{\"example\":[{\"customer\":{\"firstName\":\"tom\"}},{\"customer\":{\"firstName\":\"dick\"}},{\"customer\":{\"firstName\":\"harry\"}}]}","payloadType":"json","x":250,"y":3100,"wires":[["51466519ddf4a14b"]]},{"id":"51466519ddf4a14b","type":"switch","z":"da8a6ef0b3c9a5c8","name":"","property":"$$.payload.example[-1].customer.firstName","propertyType":"jsonata","rules":[{"t":"eq","v":"harry","vt":"str"}],"checkall":"true","repair":false,"outputs":1,"x":430,"y":3080,"wires":[["a81d87f562b74deb"]]},{"id":"a81d87f562b74deb","type":"debug","z":"da8a6ef0b3c9a5c8","name":"debug 225","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":650,"y":3120,"wires":[]}]
$$.payload.example[-1].customer.firstName