Every journey is designed to engage with a specific marketing list. This means that all the contacts on the marketing list are going through the journey.
When contacts finish their journey, they will not continue to the next journey.
To transfer contacts between journeys we will need to create a new marketing list that will contain the contacts who have finished the journey. On the contact's screen create a marketing list that will contain the next journey you would like to apply on the contacts. For example, create a marketing list for contacts who haven't made a purchase and a marketing list when purchased. This will transfer the contacts from one journey to the other as soon as a contact made a purchase.