Hallo Rouchaittuenn42
You obviously missed the point that you are discussing with other fellow passengers in this public Internet community, therefore we can’t allow anything anyway.
As a general rule of thumb, already issued tickets can never be altered afterwards. Some can be cancelled/refunded, but this doesn’t apply to saver offers, where you are bearing some risks as a caveat for the offered good deal according to the GTC inherently accepted with the purchase. (There are actually a few exceptions allowing a SDP refund which could be war related, such as medically confirmed inability to travel, but those would be far less pleasant for yourself or for your next of kins…)
Since you’re arriving one day earlier than initially planned, simply try to make the best possible use of your SDP by traveling as much as possible across the country that day after your arrival.