In order to add collaborators to your Galleries, you must first invite them to be a team member in your workspace.
There are 2 ways to add collaborators to your galleries:
While creating a new gallery
While you create a new gallery, the option of Add Collaborators appears in the new gallery pop up. Toggle within the list of your team members and simply click on the member you wish to collaborate with for that gallery.
After a gallery has already been created
In case you wish to add more collaborators to a previously created gallery, then click on the gallery you require.
Select the option of Collaborators from the options on the left of the screen.
Next, navigate to the top right corner to select the Manage Collaborators button.
A pop up will appear that will give you the list of your team members earlier added in Team tab.
You can search for a particular team member, select that member to be added as collaborators.
Deleting a collaborator from a project
All you have to do for deleting a collaborator is to select the option of collaborators in the gallery, and navigate to the top right corner to select the Manage Collaborators button.
Simply deselect a previously added collaborator to remove him/her from that particular gallery.