What is the amount that must be returned to the shop owner after a sum of money was stolen from him in 1992 CE, taking into consideration the decrease in the currency's value? And should the amount be multiplied to equal its current value? And how can he be informed of this theft?

You are required to return the money you stole to its owner. You should estimate the amount that you believe will clear your conscience. You are not obliged to inform him of your deed; rather, what is obligatory is to deliver the money to him by any means possible. The obligation is to return the equivalent amount, no matter how much the currency's value has decreased, as long as it is still in circulation.