Fixed Asset add to cost

Hello,

I have question related to FA. There is an asset whose original cost was 6500 over the period the asset was depreciated fully. By mistake the user made add to cost of the same asset which does nothing but changed the current cost and depreciated it with same amount. The net book value is zero.

How can we reverse this. So that current cost is show right which was before the add to cost?

When we did add to cost where did this hit at GL? where can i check this?

Please tell me the process of reverting this back to original.