the problem is if you changed the online return, that's what will be there for next year which can cause issues.
however, you have several options:
1) you can change your online return and subtract the lesser of your UC comp or $10,200 on schedule 1 line 8 but then you'll have to remember to change it back
2) you can take your taxable income and subtract the lesser of your UC comp or $10,200. then go to the tax tables or tax rate schedule in the 1040 instructions https://www.irs.gov/pub/irs-pdf/i1040gi.pdf and compute your tax. compare your new tax line 24 to your old tax line 24
