The reason you cannot currently move the client's Retirement event to Year One or delete it, is because of the existing 'Pre-Retirement' stage to which the Retirement event is connected, or 'linked', i.e. the 'Retirement' event is acting as a 'boundary' between the one (Pre-Retirement) 'stage' and the other (Retirement).
In a situation where an individual is either already retired, or is retiring in Year One of the plan, this effectively negates (from the software's perspective) the existing 'pre-retirement' stage. In order to drag the individual's Retirement event to Year One or delete it, therefore, one will *first* need to remove/overwrite the 'pre-retirement' stage.
Now, note that one cannot delete a stage outright, but you can overwrite an existing stage with an adjacent stage. This involves clicking on the Retirement stage, select the Start event in the Timing section by clicking on it and setting this as the Start Event, then click Done.
Click Continue to the warning message which appears.
Once you have overwritten the pre-retirement stage, you will have freed the Retirement event(s) from being used as stage boundaries. You will then be free to move one, or other of the Retirement events to Year One of the plan, or even to delete the events if they are no longer needed.