[webmaher]

      <rating name="metacritic" max="10">
            <value>8.6</value>
            <votes>60</votes>
        </rating>
        <rating name="tomatometerallcritics" max="10">
            <value>9.7</value>
            <votes>400</votes>
        </rating>For movies this work excellent
How can I get this rating also for all my series?

The option is in the TV Preferences, RTTomato ratings, series & episodes
But it will depend if the data is available to get for the series. This is out of our hands, up to OMDb. 

You are right... I made test for serie Big Little Lies and no data ...
Thanks 4your help