Hi Shriya,
For your scenario you can create the asset as a "post-capitalization". This functionality exists exactly for situations where you have to create assets that normally should have been activated in a previous year already.
When you create the assets in AS01 you can tick the flag "post-capitalization". Then you will be able to enter an activation date in the past. You can also set the original depreciation start date on the "Depreciation Areas" tab.
Afterwards you can activate the assets with a post-capitalization posting (transactions ABNA or ABNAN). There you can enter the "original value date" for the posting. This date can be in the past (actually, it is supposed to be in the past. Otherwise you could just use any normal posting transaction). With the post-capitalization posting, the asset will already receive the depreciation amount that was "missed" for the past years (You can either have it calculated automatically by the system or enter it manually). No manual or unplanned depreciation posting will be necessary.
Best regards, Michael