You can go to different time era with the time glitch in Pokemon sword and shield which I got most of my Pokemon from. All you got to do is go to a raid den And see the Pokemon and if it is not yours then you should go to Invite others, Go to system settings, go to time and switch it out for a different time. Then you should cancel it and then Your den will reapear with a different Pokemon. IF you get the Trevenent you want then finish the raid and switch the time back. If it fails repeat the process. You do not need a nintendo switch online membership to do this because you aren't actually inviting people.
Warning: Might give you a penalty! But has not given me one.