Ok, you should get a few tubs and obviously the bettas. Maybe some plastic containers or a temporary breeding tank like five to 3 gallons. Put the female in a plastic clear water bottle and or get a clear small container for her and put her in the tank yet in the water bottle/ container in the tank and let the male in the actual tank. After a week or so (or a few days) let the female out no that they both know neither of them are a threat and they’re in the mood. Then they’ll get to know each other and mate. Make sure there’s a bubble nest. After the female lays her eggs, and there in the bubble nest and fertilized, remove him and you CAN keep the female or male, but it’s suggested to remove both. After they hatch put them in. A temporary baby betta tank away from adults. After they’re old enough to go into tanks alone and or with adults, you don’t have to do anymore work except the basics like feeding and water changes. Then repeat that process for more betta breeding.
Just be mindful that they produce LOTS of fry, who require a lot of time, live food, space and effort to grow to a sell-able size. And most petshops are paying peanuts for their bettas so it might be best to try find potential buyers before breeding them. And you'd want good quality/healthy stock and unique patterns etc too