That is not possible normally, except if customer service grants you some kind of extension or voucher.

Did you buy it as mobile pass and via site? ONLY seller itself can do any changes, if allowed. In this case I doubt if there still is the old ´covid-allowance´ valid-but you never know.

Service is overburdened with work and does/can only handle the real urgent things with passes-refunds and all that takes monthes.

Maybe someone can flag it for you-there is a special customer form and you must always indicate for what day it is intended-as they handle requests in that order.

OTOH: passes have 11 monthes to be made active, so having a newborn (congratulations!) should have been known then, in my opinion.

Unless you bought the pass on a special sale, the pass is refundable. The conditions of your pass should either be in your confirmation email, on the invoice or somewhere on your Interrail account.

Here is information about the refund and exchange policy.

https://www.interrail.eu/en/interrail-passes/ordering-info/refund-exchange-policy