Unregistered link relationship: search

After 2 days searching this forum and elsewhere on the web,changing theme, changing, headings, changing text etc. I am tearing my hair out.

I only have a simple on-line blog https://thersr.wordpress.com.

I want to add it via an RSS feed to a web forum. https://www.rmweb.co.uk/community/index.php?/blog/manage/?section=settings&act=rssimport&blogid=1790

I get an error message: RSS feed error: XML error: Undeclared entity error at line 10

I checked the url through feed validator at RSSboard.org and get:
This feed is valid, but interoperability with the widest range of feed readers could be improved by implementing the following recommendations.

?line 27, column 142: Unregistered link relationship: search (2 occurrences) [help]

… om/osd.xml” title=”Tales from TheRSR” />

Line 27 read as follows: <atom:link rel=”search” type=”application/opensearchdescription+xml” href=”https://thersr.wordpress.com/osd.xml&#8221; title=”Tales from TheRSR” />

I have no idea what all this means. All I want to do is publish my blog to the website above. I see that other WordPress sites are linked to the website for example: https://rstower.wordpress.com/

Would really appreciate any help. Please bear in mind that I am a very simple and, (increasingly hairless)user! ??

Many thanks

RichardS