Updating Caseid

I have a few cases which were imported from external sources and eventually, rather inadvertently became duplicate. Unfortunately, in some cases we have registration one caseid and followup forms on other case id. So is ther anyway, i can update the case id i registration for followup forms

Or is it possible to transfer data of from one form id to another id

Your issue is really not clear.
How can you have one case id in registration and some other case id for the same beneficiary in follow-up? If this is the case, then according to CommCare they are 2 different cases because if it is the same case then it will have the same caseid, no matter where you transfer it.
As far as I know, if you import a case manually from an external source, CommCare creates a caseid on its own.
No, there is no way to update or change the case id but you need to check again because if the caseid in the registration and the follow-up are different then they are different cases, because the caseid will always be the same for the same case.

I think i did not spell out my case clearly. Sorry for that. I will explain with an example. I have a registration in an external form. SO I import it in CommCare. Si get a caseid but no form related data. Lets assume its caseid as 1. Somehow the that case was directly registered in CommCare also. Lets assume its case id as 2 SO now we have two caseid's for one participant. We have to do three followups A, B and C. Followup A is done on caseid 1 and followup B on caseid 2. Now how to solve this issue