you need a spritesheet, and json file generated by aseprite. create a new resource in godot of the type AsepriteAtlas. configure it as needed:
[Export] public string AtlasName = "TestAtlas";
[Export] public string OutputPath = "res://textures/whatever";
[Export] public string OutputFileNameFormat = "<atlasName>~<filename>.tres";
[Export] public string TexturePath = "res://textures/whatever";
[Export] public string JsonPath = "res://textures/whatever";
run the AsepriteAtlasGeneratorDock scene with the scene running, select your AsepriteAtlas resource.
AtlasTextures will be generated.