First of all, "Missing microdata for condition" is not an error and can reduce some impressions, but it does not mean that the product is disapproved. 

Any error that is about "Microdata" is not about anything wrong with the feed. Microdata errors arise out of either incomplete or wrong implementation of "Schema.org's Product
By default, the app sets all the product conditions as "new" in the feed because more than 98% of our merchants are selling all their products in the brand new condition. If you are selling any Used or Refurbished product, kindly update the condition value for the product by using the Bulk Edit feature of the app. 

For Products in "New Condition", use the code mentioned below: 
http://schema.org/OfferItemCondition" content="">">">http://schema.org/NewCondition"/>
For Products in " Used Condition" use the code mentioned below:
http://schema.org/OfferItemCondition" content="">">">http://schema.org/UsedCondition"/>
For Products in " Refurbished Conditionuse the code mentioned below:
http://schema.org/OfferItemCondition" content="">">">http://schema.org/RefurbishedCondition"/>

Once you have implemented the markup, you should test the Product Page URL on Google's Microdata Testing tool.

It should show results like this on this URL. (This is the result of ideal markup implementation).

Note: Once you have implemented markup for Item Condition and tested it successfully in the Structured Data Testing tool of Google, wait for up to 10 days to have error counts coming down as these error corrections are recorded when Google crawls your product pages again.