Number of Asset Units in Tax Book

Hello, our tax book has active assets that have been previously retired in the Corporate Asset book.  Some of the assets have multiple units. For example asset #1 has a cost of 1260 and units =6, for a cost of 210/unit.  If one of the units is scrapped, I know that we can retire the cost of the scrapped unit (210).  The asset however remains showing 6 units.  Is there any way to reduce the number of units so that the units are correctly shown in the tax book?  After retiring the cost of 210 in the tax book, I