Open the Messages app on your iPhone
Find the conversation you want to print
Take screenshots of the messages you want to print
Save the screenshots to your Photos app
AirDrop or transfer the screenshots to a Mac or PC
Open the screenshots on your computer
Print them from the Photos app, Preview, or your image viewer
Use iCloud Messages or a backup if you need more messages than fit in screenshots
Export the messages with a third-party app if you want a formatted transcript
Print the exported file from your computer