Question for shiny hunting

Hello everyone! First time hunting for a shiny Pokemon and I was curious about something. So to my understanding when you find a shiny Pokemon it won’t de-spawn unless you knock it out or you scare it off. I’m hunting for a shiny Ralts using the fast travel method and wanted to know, let’s say I found a normal shiny ralts and wanted to get an alpha version of it instead, can I continue to fast travel in the hopes that it’ll change into an alpha shiny ralts or would I have to just be lucky enough to run into a shiny alpha Ralts? Appreciate the answers and if you have any tips for me then I’m open to hear them. Thanks in advance 🙏🏽