if I have already admob account ,when i set up a google ad manager by kodular, set up not compelete any way ,is there is any relation between incomplete setup and having admob account?
the 2nd question : is there is free working admob account compatible with kodular ?
This issue is being faced with many ad mnaager new users its not particularly related to admob in any way but ad manager is related to adsense account at some point also check that you dont hold a old ad manager account it can be causing issue !
regarding the account not created kodular team is working to fix it also currently ad manager is facing issue with banner ads
if you want to use admob, unity or any other ad provider you can simply buy a ad extension+ kodular premium to show ads in your app or use a free extension+ kodular premium to show ads
If you have an other doubt feel free to ask! 
is there free working admob extention ?
Yes there is search for it in community and you will surely find 1 !