hello Ive got and interview at a company in Japan next week and im so nervous.
They told me that my Japanese ability is key so I was wondering if anyone has had any experiences having to demonstrate their
Japanese for a company.
Ive passed the N1 exam and the job is mostly an excel worksheet based job so im not going to have to talk with costumers.
Im thinking they just want to know if I can communicate with co workers and that I have some dedication to staying in Japan.
I just feel really nervous because I really want this job.

If your keigo is bad or you don't feel super comfortable with it, then don't use it. Stick with the normal stuff, they aren't likely to dock you for that but if you open up with keigo and fumble all over, you just look bad.

Remember, too, that a big big part of Japanese job interviews is making sure that you'll fit in with your co-workers, and that's emphasized even more if you're not Japanese. If you can show that you fit in with Japanese coworkers, some shortcomings in your Japanese will be forgiven.