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See the code e.g. UBC-97 to calculate amplification factor Ax. Max Ax = 3.0. This Ax you will multiply by 5% (0.05) and input in response spectrum cases/static earthquake cases. To calculate Ax, you need maximum and average story displacements at CM. You can export this data from ETABS Tables to EXCEL for static earthquake cases (Don't use spectrum cases for this). Once in EXCEL, you will see column named 'Ratio'. This will be Max/Avg displacement. Sort this out to find values more than 1.2. These are the locations you need to amplify torsion. After checking which stories you need to amplify torsion in, use the amplified torsion value for e in response spectra cases.