rotting window frame

I live in a 80 yr old house. Unfortunately the basement window is right at grade level and as a result the wood frame comes in contact with the concrete and the other day I noticed that the wood was split. When I touched it, I noticed it was wet and when I pushed on the wood, I created a hole. Unfortunately the wood is still wet and given that winter is just around the corner, I am not confident that it will dry out before winter. I know that I need to fix this, but have no idea whether I can just carve out the rotted wood and then I can just fill the cavity with putty/caulking/foam insulation and then cap.

Looking for some guidance on how to fix this and whether there are other resources that can help walk me through this.

Thanks