Hello Jainish,
Yoast SEO no longer uses the frequency field in the XML sitemap and it was removed from Yoast SEO v3.5. Google has?said publicly?that they don’t use them on most sites. And as such, the relevant optional field was removed from the Yoast SEO generated XML sitemap.
That said, you won’t need to change or add the frequency/priority in the XML sitemap as Yoast SEO automatically ping Google and Bing crawler as soon as you update or publish a page on your site. So, if you update a page frequently, Google crawlers should aware of the relevant changes at the right time automatically for you once they read the sitemap.