When you revalue an Asset, you are creating a Journal Entry with two balancing Journal Items. 

Your Asset goes up or down in value (first item) and the same amount is posted in a second account related to the reason for the change in value (second item). 

Depending on your accounting setup and the nature of the revaluation, this could be:

A Revaluation Reserve account (under equity).

A Gain/Loss on Revaluation account (under income/expense).

Some other adjustment account, depending on whether you're increasing or decreasing the asset’s value.