These are just sample examples. Writers here arrange these in different ways that works best for them and that's perfectly fine. This gives you the jist and an easy thing to copy and paste.

If cross posting from another platform:

"First published in <insert publication's name here> on Medium/Substack/Facebook/WordPress/Tumblr" etc..
Then link the publication site to its name.

If cross posting from your personal blog/site:

"First published in <insert publication's name here>." Then link to your blog/site.

If submitting a reworked article from another platform:

"Revised article first published in <insert publication's name here> on <date> from my personal blog/Website name/Medium/Substack/Facebook/Wordpress/Tumblr" etc.
Then link the publication site to its name.

Place this information at the bottom of your article.