Issue
You need to mass update Salesforce records to get them to sync into Marketo.
Solution
Use the Salesforce provided Data Loader! This is a tool Salesforce provides for such occasions. Here's an article from Salesforce with more information. For any questions regarding this tool, please seek your Salesforce Admin or Salesforce Support as they will be the best resource to answer those questions!
https://developer.salesforce.com/tools/data-loader
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