I Got This (2018)

Doting dad Chris learns that the three-year-old girl he's been helping to raise isn't his. Not only that, but her mother doesn't want to marry him, and might move out of town with the child, feeling she has no better options. He convinces her to try to figure out who the real father is, in hopes of a child support settlement that will allow them to stay. So they stalk three men who she slept with during the month before she got pregnant, and find inventive way to get samples of their DNA.