An excellent resource for the MIXED (not "MIX") procedure is
https://www.sas.com/store/books/categories/usage-and-reference/sas-for-mixed-models-second-edition/prodBK_59882_en.html
I suggest that you first make an effort at the code yourself. If you have questions after that, then you can post your code, a detailed description of your study, and an example data set.
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