What don't you want from Extra? Zotero stores certain fields there that don't yet have official fields, but it generally should be valid data that belongs in citations.

To clarify: when I added the citations to zotero, a lot of random data was stored in the 'extra' field. I don't mind it being there, but the current style I am pulls these data into the bibliography. But in the CSL of the style there is not field called 'extra'. I want to delete from the style but can not find it. Thanks a lot

for example, publisher information, which should not be included in the required bibliography style for a journal

It'd still be helpful to get the answers to the questions above to see if Zotero is importing something it shouldn't, but the basic answer to the question is that data entered as key: value (e.g.: publisher: SAGE) into the Extra field is passed on to citation styles as regular variables. There's no distinction between those variables and variables that come straight from Zotero fields (so no need to exclude them), so your only options are to
a) remove them from Zotero or
b) exclude them from citation styles, along the lines of

<choose>
<if type="article-journal article-newspaper" match="none">
<text variable="publisher"/>
</if>
</choose>