Rather than buying pineapple juice, you may use the juice drained from the can of crushed pineapple.
Combine in a small bowl and stir until the sugar is dissolved:
Place in a medium bowl:
Stir the pineapple juice mixture into the milk. Pour into an ice cream maker and freeze as directed.
Transfer to a container with a tight-fitting lid and freeze for at least 4 hours to harden.