Not sure what your issue is ... did you sell the new stock yet ? Only thing you need to report on the return is the fractional share that was sold and usually you will leave a zero cost basis for that transaction and leave all of the basis with the stock you still own thru the reverse merger.
For instance if you owned 25 shares of the old stock for $1 cost basis each for a total of $25 then you now have ONE share of the new stock with a $25 cost basis. Until you sell the new stock you have not realized any loss so nothing is reported on the tax return.
