Hello,
Thank you for contacting Rank Math, and sorry for any inconvenience caused.
I have tried accessing your site but it’s resulting in a 403 error.

Please check when the Google cache was updated for that page:
a. 
b. 
If the cache date is from before adding the new meta description, then you just have to wait for Google to re-crawl and re-index the page with the new info. If the date is after you made the changes, then you just have to wait it out and there is no further input needed from your end.
Do note that if everything’s fine and Google still decides to show a different meta title/description for your search keyword, there is nothing you can do as Google sometimes ignores the custom meta info altogether and show something from the page’s content that matches the search intent better.
Here are some of the common reasons Google might not use the meta description you provided:
– The meta description is not relevant or useful (ie, just a collection of keywords).
– The exact same meta description is provided across a large number of pages.
– The meta description doesn’t match what the user is searching for, but other content on the page does.
There is a whole article dedicated to this on SearchEngineJournal:
https://www.searchenginejournal.com/google-offers-suggestions-for-avoiding-meta-description-rewrites/359884/
Here is an example showing Google changes title depending on the keyword used:

&

The best you can do is optimize your meta tags to try and match the intent of the search/keyword.
For your sitemap:
I have validated your sitemap with https://www.xml-sitemaps.com/validate-xml-sitemap.html and it got validated successfully.

Please flush the Sitemap cache by following this video screencast:
https://i.rankmath.com/pipRDp
Once done, re-submit the sitemap_index.xml in Search Console and wait for Google to crawl the sitemap.
Hope that helps. If you have any further question(s), please let us know.