How to enroll contacts more than once into a Journey?

This article provides you with a step-by-step guide for allowing contacts to go through the journey multiple times

You can choose the one-time enrollment option for onboarding journeys. The multi-enrollment option can be used for journeys created for cart abandonment reminders or order-placed campaigns.

Note - 

Step 1: In the journey builder, setup your journey and go to Review and Publish step and click on Journey Settings from the right.

Step 2: Contacts entry to journey will be selected as One Time by default for all the journeys. You can choose More than one time and click Save for the contacts to be able to go through the journeys multiple times.

That's it. You're all set! Now the contacts will be enrolled in the journey as many times as they qualify the criteria set in the journey