Enabling sharing for a Zoom Meeting can only be done by the host.
There are two ways to ensure that the meeting has screen sharing capabilities.
Update the Profile Settings
Update in a Zoom Meeting
The host can modify their Profile settings within Zoom to configure this as always available.
To do this, navigate to the Profile Page
And under the In Meeting (Basic) section, toggle on the Screen Sharing.
Note there are additional parameters that you can set regarding your Zoom meetings and screen sharing.
If the Zoom meeting has already started and the sharing privileges have not been selected for the participants, the host can modify this setting for this meeting.
If the screen share is completely turned off, the host will need to modify the Profile settings from above and restart the Zoom Meeting.
Under the Security button on the hosts client controls
The following options will appear, and the host can select to allow participants to Share Screen