Keldeo
First, find his island and cook the Curry with Virizion, Cobalion and Terrakion in your team.
Check that Keldeo can spawn at the center of the island.
Force Keldeo to despawn by flying away into another place.
Return to the Keldeo Island, and place your pg in the northern side before the tree.
You need to find a spot where Keldeo doesn't spawn yet, while if your pg takes few steps forward, Keldeo spawns.
As for example, you can position your PG in that location:
Save the game while you're on the bike.
First, download the Sys-EncounterBot: https://github.com/Manu098vm/Sys-EncounterBot.NET/releases.
Go in the Hub tab and select Keldeo under SWSH_Encounter.
Scroll to ConsoleLanguage under FeatureToggle and set it to your language.
Scroll to StopConditions and set them according to what you're looking for.
Please note that Keldeo is Shiny Locked, but it can be hunted for IVs, Nature and Marks.
Go back to the Bots tab, select SWSH_EncounterBot, click Add then Start All.
If you'll find always the same Keldeo (same IVs, Nature etc), force it to despawn by flying in another place.
Alternatively to the previous setup, you can also use the OverworldScan Bot to read the overworld data for the encounter.