Simply “killing” a paid package that has already been purchased with a new benefit package and thus declaring it invalid is actually not possible.
In my opinion this is a clear concept or program error.
Until Swisscom realizes this, you could, as a workaround, simply purchase the additional data you need from outside Swisscom.
If you have a dual SIM cell phone, for example, simply add a prepaid from myMucho as a second SIM (also uses the Swisscom network) and, if necessary, activate the DUONANO package for CHF 4.90/month.
This would mean that you would not only get the 500 MB of extra data you want, but also 75 minutes of free telephony, which cannot be deleted by Swisscom.
P.S.: By the way, dual SIM is always a good thing and you should definitely take it into account every time you buy a new cell phone.
Hobby-Nerd ohne wirtschaftliche Abhängigkeiten zur Swisscom