Try to follow the guide here but should be able to skip LID manip and getting Kenya. When you get to the lighthouse don't do the lighthouse section, instead surf immediately to Cianwood and release your Gatr that knows surf.
https://www.speedrun.com/pkmngscext/guides/gj059

After a few practice runs, can try this more advanced guide:
https://pastebin.com/UUxLzxzL

Video reference. Major deviation starts after Morty's gym just after the 58 minute mark.
https://www.youtube.com/watch?v=uaGprf8mRmU