Enable HD videos for attendees

Welcome to the Zoom Community, @AmSingh.

Your question is a little ambiguous.  Which videos are you wanting to be in HD?

• Attendee camera video?  Attendee cameras are never activated in Webinars.
• Screen share video? Screen Sharing is always shared in the native resolution of the shared source.
• Panelist camera video?  This is enabled for webinars according to the following Zoom Support article:
  https://support.zoom.com/hc/en/article?id=zm_kb&sysparm_article=KB0057547

Note that there are prerequisites which might limit you to 720 instead of 1080.  Note also the requirement in the third paragraph that it must be enabled by Zoom Support; make your request via a Support Ticket here.

I hope this helps.