In order to share your location to a private group, you must first be a member of or create a private group. If you have not done that, please follow the instructions in this article.
And if so,
1. Navigate to the private group you want to share to where you should see a private group map.
2. Next, initiate a Share by tapping on the beacon in the upper right-hand corner.
Note: if you are not yet sharing to the group, you will get the following message. Click share location.
3. Next, the Glympse configurator should appear. You will notice, however, that you cannot edit the recipient, as it will always be the group. Configure the options, if desired: destination, duration and/or a message. Then tap the arrow in the upper right-hand corner in order to share your location in the group.
4. You should then be returned to the group map where you should see your Glympse.