You said: 'I tried to use Command(APDL) Scripting in Workbench which includes iterative heat load using *do loop. I want to extract the temperature in /POST1 during each iteration and use it to update input under /SOLU.'
So what do you want to get from POST1 - is it temperature?
And what do you want to update (BFE,,HGEN?) using the post1 results above in your input?
Yes there are some ways, but the way you do it is wrong as you can see from the error message (BFE is a /PREP7 or /SOLU not /POST1 command), and it is outside what we (Ansys employees) can help with here as it requires extensive apdl scripting - perhaps some other users can help, but if you answer in detail my questions, there might be an easier way of doing what you want.