What would you do if you try the free online plagiarism-checker and you discover that it detects your original paper on the publisher site or on other sites as a match.
It depends on what algorithm the software uses. Is it capable of distinguishing an original publication text section from subsequent publications in which that text is cited? I frequently write analyses in which I quote extensively from published opinions and reports, in order to build my case, but I ALWAYS make it quite clear who wrote the text, where it came from, (with an active link to the original), and the quotation is usually indented, and if possible in a different text colour or style from the main text of the anlayis. So a plagiarism-checker might report the insertions as 'stolen' when in fact they are there to emphasise the original authors' opinions and findings - an actrive citation and not a steal.
But if the reported copy of your own work is NOT shown in this way, and appears to be republished with the apprent intent of boosting the plagiarist's own reputation rather than yours, then report it in strongly worded terms to the Editor of the Journal publishing the material, and demand that the offending article be retracted. In extrme circumstances, try somewhere like the 'Retraction Watch' website, where they expose fraudulent science publications. Remember, modesty is for suckers!