Not necessarily a guide, however, I noticed this popped for me right after completing all events in Kashyyyk. The reason for this is because the only "event" in Kijimi from my knowledge is the story mission "C-3P-Oh no!" which belongs to Episode IX - The Rise of Skywalker as the third mission. Just to clarify for those who were as confused as me at first.
In Short, Kashyyyk is the primary target for this achievement, and completion of the story mission "C-3P-Oh no!" on Kijimi in Episode IX automatically should grant to the 100% for Kijimi.