I don't use mwan3, so no, I'm not going to be able to help. However, you can read the mwan3 documentation.
https://openwrt.org/docs/guide-user/network/wan/multiwan/mwan3
Also, this is now veering off-topic relative to your original question. I'd recommend a new thread for mwan3 questions.
If your problem is solved, please consider marking this topic as [Solved]. See How to mark a topic as [Solved] for a short how-to.
Thanks! 