I just started my post doc and currently writing a paper but I don't have any professional writing experience. Is there a learning curve or forums that can help with improving writing skills? E.g. I want to rephrase "The review paper published recently talked about the wide range of.." into more professional sentence. How can I get help on this?
Many universities have a "writing center" or equivalent that will typically be your best starting point, since it has people who are paid to sit down with you in person and help you solve this problem.
If your institution does not have such, there are massive numbers of online scientific writing courses that may help. Personally, I have found Jean-luc Doumont particularly helpful, and especially his "architectural" view of writing. Different people will find different resources fit their personal learning styles best of course.
Next, if at all possible, make sure that you are partnering with mentors or co-authors who are good at writing.
Finally, read! The best way to understand what works in communication is to be a reader and learn what works for you.