How can calculate Available to reserve Lot bases

How can calculate Available to reserve Lot bases.

There is no Lot information in the INV_reservation and also in to inv_material_txns.

In UI Lot onhand is showing 900 and available to reserve is 790. When checking in the Inv_reservation is 100 quantity record is there but lot field is blank.

When checked in inv_material_txns this having 2 record 100 and 10 quantity that is correct but there is no lot information and lot is showing blank.

I need to calculate ATR based on lot