Check these article.

（1）yahoo_ydn_conv_io Value unique to the customer’s account. Must not be changed.

（2）yahoo_ydn_conv_label Item that identifies a tag. Must not be changed. Note that tags automatically migrated from old format YDN tags (supplied prior to September 2014) will be blank.

First setting of conversion tracking for website - Help - Yahoo! JAPAN Ads

Get and install a site retargeting tag on your site - Help - Yahoo! JAPAN Ads