I have tried to find any config parameters for this but couldn't find.
There is no argument like confidence that you can pass to the pytesseract image_to_string(). The list of accepted arguments are:
image,
lang=None,
config='',
nice=0,
output_type=Output.STRING,
timeout=0
You can find the same in their official repo: https://github.com/madmaze/pytesseract/blob/master/pytesseract/pytesseract.py