If you have admin access on your CommCareHQ project space, you can transfer/re-assign cases that are registered on one Mobile Workers case list to another Mobile Worker through the Data tab available at the top of CommCare HQ.
You will see the following messages when a case has been successfully reassigned (a blue updated tag in the owner column, and an orange Out of range of filter message for date Last Modified):
When you move cases to a new user, you are ONLY moving the "case"– not the individual form submissions. It is strongly recommended that you NOT delete any "old" users if you want to be able to do any sort of data analysis. Individual form submissions will always remain linked to the user that submitted them–even if that user is no longer active. If you want to hide an old user's data you can "deactivate" the worker under the "settings & users" section of CommCareHQ.
When you transfer cases that belong to mobile user "Lalita" to mobile user "Sheela", the transferred cases will be reflected on Sheela's case list on her phone once her phone syncs to CommCareHQ. On the server side, form submissions made by Lalita will always be linked to username Lalita because she completed those forms. The change will however be reflected in the case exports, which will show Sheela as the new owner of the case. Any new form submissions completed by Sheela for the transferred case will reflect Sheela as the username in the forms exports. The old submissions for that case will still remain under the username "Lalita"