Since you indicated on your tax return that you could be claimed by someone else, you are not eligible for a stimulus payment. If you met the requirements to be claimed by someone else, you should have checked the box even if someone else did not claim you.
If you do not meet the requirements to be claimed by someone else, then you will have to prepare, print and mail an amended return form 1040X to uncheck the box that you can be claimed by someone else. The 1040X must be printed and mailed. It can't be efiled. Here is a link with more information about it: https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed
If you don't know whether you meet the requirements to be claimed by someone else or not, see the requirements below for each type of dependent:
Requirements for a Qualifying Child Dependent:
1. The child must be your son, daughter, stepchild, foster chld, brother, sister, half brother, half sister, stepbrother, stepsister, or a descendant of any of them.
2. The child must be (a) under age 19 at the end of the year, (b) under age 24 at the end of the year and a full-time student, or (c) any age and permanently and totally disabled.
3. The child must have lived with you for more than half of the year. Temporary absences while away at college are considered living with you.
4. The child must not have provided more than half of his or her own support for the year.
5. If the child meets the rules to be a qualifying child of more than one person, you must be the person entitled to claim the child as a qualifying child.
6. The child must be a U.S. citizen or U.S., Canada or Mexico resident for some portion of the year.
7. The child must be younger than you (or your spouse, if filing jointly) unless disabled.
Requirements for a Qualifying Relative Dependent:
1. The person cannot be your qualifying child or the qualifying child of any other taxpayer. A child is not the qualifying child of any other taxpayer if the child's parent (or any other person for whom the child is defined as a qualifying child) is not required to file an income tax return or files an income tax return only to get a refund on income tax withheld.
2. The person either (a) must be related to you or (b) must live with you all year as a member of your household.
3. The person's gross taxable income for the year must be less than $4,200 in 2019.
4. You must provide more than half of the person's total support for the year.
5. The person must be a U.S. citizen, U.S. resident alien, U.S. national, or a resident of Canada or Mexico.
