Once I upload a final version of a DMP and other research plans to Zenodo, do I need to update this first final version from Zenodo or from Argos?

Both options are possible according to how you have deposited the DMP or other research plan in the first place. If you have deposited your DMP or other research plans with a token (i.e. from the ARGOS account on Zenodo), then you won’t have editing rights on the Zenodo record, but you will still be able to make changes on ARGOS by starting and depositing a new version of the published DMP or other research plans. However, if you have deposited your DMP or other research plans using your own account on Zenodo (i.e. login to Zenodo with your own credentials), then you are able to also make minor changes, e.g. on the title of the DMPs or other research plans, directly from the Zenodo interface.