You can only change this if you ask the payer to correct the Form 1099-R, they refuse, an you then submit a substitute Form 1099-R (Form 4852) substantiating that you paid $100 rather than $200. Increasing the box 5 amount generally correspondingly decreases the box 2a amount.
Note that box 5 generally only shows the amount of nontaxable return of premiums that are included in the gross distribution. If this is reporting some amount of regular periodic payments made to you, each distribution contains only a portion of your basis in premiums paid.
You can only change this if you ask the payer to correct the Form 1099-R, they refuse, an you then submit a substitute Form 1099-R (Form 4852) substantiating that you paid $100 rather than $200. Increasing the box 5 amount generally correspondingly decreases the box 2a amount.
Note that box 5 generally only shows the amount of nontaxable return of premiums that are included in the gross distribution. If this is reporting some amount of regular periodic payments made to you, each distribution contains only a portion of your basis in premiums paid.