Do you mean these values are in the Field: Brand Segment?
Which one is correct?
In theory, SFDC will accept any value into the picklist field, especially via a tool like Marketo. You can use Marketo to find the errors and correct them.
Kate Conlon Roberts, if you know which data value you want to be canonical, you can easily use a smart campaign to correct this as Josh mentioned, e.g.
Brand Segment = Career Webschool
Change Data Value, Brand School - New Value = Career Web Schools
This will fix it right up. However, you should also identify where the different values are entering your system. If it is a free text field in SFDC, consider making it a picklist to put some validation on what users can input.
If the discrepancies arise in Marketo, you may have a rogue form field option or flow step that is causing it.
Without fixing it at the source you'll continue to have the problem.