Hi,
The field "Account ID" holds the joomla user id and the field "userid" holds the Acymailing subscriber id. You can't import data into these fields. The first one is retrievd from Joomla and the second one is automaticly assigned by Acymailing.
I suggest you create a new custome field for the VM id.
Please note that the support for v5 has ended by the end of January. We strongly reccommend to migrate to the current version, which is v9.
https://forum.acymailing.com/d/4694-end-of-v5-support-planned-in-january-24