Once a parcel is already in transit it's not usually possible to make changes to the address, sorry!
So what can be done then?
you can ask the courier to drop the parcel at your closest collection point instead. Courier tracking and contact details will be contained within your Shippit email notifications
the depot can hold your parcel for a depot collection. Please contact the courier directly to book this in.
ask the depot to hold your parcel until a redirection can be arranged (not always possible). The courier will be able to advise if this can be done free of charge, if not you'll need to contact the sender directly for authority as they will need to cover the charges!