Sometimes for better clarity and good organization, you may wish to connect one sitemap to another sub-set of sitemaps.
The is easy to do (with the Editing Pro feature)
Step 1: Create either a New Child Page or Folder/directory from the Sitemap you wish to link from.
Step 2: Edit the Page
Step 3: Enter the Sitemap's Name
Step 4: Upload a screenshot from the 2nd sitemap > Main Page
*Note: you can get this from here.
Step 5: Open the second sitemap and Copy the Shared Map Link into your Clipboard
Step 6: Paste this link into the new page you created:
Done!
PRO Tip : You should also create a backlink on the second sitemap back to the main one too!