How can I compare my power meter accuracy?

I have suspicions that my 4iiii left PM is over-reading my watts. I currently have a kickr core and assioma pedals I can compare it with.

What are the steps I can take to compare them?

My plan currently is to connect each power meter separately to a device e.g. kickr core to zwift, 4iiii to my watch and assioma pedals to elemnt bolt.

My question is how do I sync all the data together? Assuming i start each ride within a couple second of each other.