Hi Joshjo,
First you should configure revaluation allowed for your depreciation area in T code OADB.
Then in T code AO90, configure account determination for revaluation account assignment.
Then in AO84 you shall define transaction types for revaluation.
Then you can use T code ABAWN for revaluing the asset.
If you want to do mass revaluation then you can create a bdc for revaluing the asset using ABAWN.
Hope it solves.
Regards,
G.Sethuraman