I haven’t had much luck preserving holy basil. One way to freeze it for stir frying is to puree it with a little canola oil and freeze it in small portions right away. It can be thawed and stir into curries as an acceptable ( to some people, myself included) way to get that wonderful flavor in December if you live where I do. I generally just enjoy growing it and using it until the first frost, then buy it at my favorite asian market until time to plant it again. Some things are just meant to be used fresh. Try the puree though, it’s really pretty good for chicken with chiles and basil and other southeast asian stir fries. Especially is you don’t have easy access to an excellent asian market.