Please read through our webpage on Bermudagrass: https://extension.umd.edu/hgic/bermudagrass
Be mindful that the herbicide mentioned only suppresses Bermudagrass. It does not rid your lawn of it, even with repeated use. Unfortunately, the grass is so tough that the only way to really get rid of it is to entirely renovate the infested area before it spreads farther. Early fall is the best time to renovate.
Here is good info on how to successfully renovate your lawn: http://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/hgic/HGIC_Pubs/lawn_pubs/HG102...