If I understand you correctly the first hurdle is that you created your games in Flash (Animate) and did not use any IDE like FDT or Flash Develop.
I guess it was easier for me to move from AS3 to Haxe / OpenFl back in the day, because I had my FDT coding workspace separated from *.fla and *.swf files, which I occasionally used as graphics libraries, if at all.
So like mentioned above you should follow the starting guide an learn how to create and compile a simple test project.
If you don’t have too much code inside your *.fla files but mostly in AS3 class files, you could try to convert a small project. That worked pretty well for me.
I „just“ had to follow the OpenFl starting guide, checked and compiled the sample project, then chose my least complex project, converted the AS3 files with as3hx and did the necessary changes (Overview · OpenFL ActionScript 3.0 Conversion Guide).
It was still a rollercoaster of emotions. Sometimes I could make huge progress in a very short time, only to get stuck somewhere else and stumble over pitfalls. But it was absolutely worth it!
And if it is not absolutely necessary, I would avoid using swf files. I gave it another try few years ago, in a small project when I was too lazy to use spritesheets, but it turned out as a dead end for me (Getting custom class names of nested MCs from SWF).
Most important: have fun and enjoy open source coding freedom! 