Navigate to Form Templates > My Templates, then click on the template in question and click the 'Share' option, highlighted below:

You will be asked to Share? Yes/No first, then you can select whether the recipient can make their own, editable copy of the template.

Select whether to share with all Teams on your subscription with 'Everyone', or click 'Configure' to select a recipient / recipients from your list of available Teams.

Note: Your original version of the template can only be edited by you. If you want to collaborate with another User on your subscription, sharing and making copies is the recommended approach.

Any templates that have been shared with you will appear under My Templates (Form Templates) with the category of 'Shared with me'. You can use the 'Show only' dropdown in the upper right-hand corner of this domain to see only shared templates:

You can engage a client/prospect with any 'Shared with me' templates, although some customization options in Template details will not be available until a copy of the Shared template is made:

In Settings > Permissions, you can control which User Types can view shared templates, share form templates, and whether they can share with Everyone:

Consider disabling 'Share form templates with everyone' for any User Type who should not share templates with the rest of the subscription