Hi @fsj117,
Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.
Unfortunately, there is no way to repair a load-bearing post. The only acceptable course of action is to replace it.
I'd suggest contacting a carpenter or handyman for their assistance in replacing this post. It must be done as soon as possible in a safe manner to ensure the structure doesn't fail.
They will likely design a way of temporarily supporting the structure so they can remove the rotted post and replace it with a new one.
Let me know if you have any further questions.
Jacob
