Hello,how do I change my form to 1099

If you only get SS it is not taxable and you do not have to file a return.  And there is no benefit in claiming dependents or deductions.   And you can't efile a return with no taxable income.  If you want to file you will have to print and mail it.  

Or you can try adding $1 of interest to let you efile.  Make up a fake 1099Int
Enter a 1099-Int  under
Federal
Wages & Income
 Interest and Dividends
Interest on 1099INT - Click the Start or Update button

Put the interest amount in box 1

If the Social Security benefits are the only income being entered on the tax return, then you do not need to file a tax return.

So no need to file a return with only my SS benefits. Thank you

That's right.  Unless you are filing as Married Joint or Married filing Separate.