Export/import between two phplist's instances

Good morning for all,
I Have 2 distinct instances of phplist and I have to transform in only 1 instance of phplist… how can I do this?
Thanks for help me.

If you just want to have all of the contacts in one system, then you should export all of the contacts from one, and then import that file into the second system. When importing, they system will not create a duplicate (using email addresses as being unique).

You will lose all of the contact history from the old system.