Hi regenx,
It helps if your Gallery is rendering a collection of your source, as opposed to being connected directly to the source.
I believe Gallery's render data in a source but they are not sources themselves, so you can't edit the data in the gallery (that I know of), you have to edit the source it's referencing.
To avoid editing your source data, you can create a limited copy of it in your app using something called a Collection.
You would need to first collect the data from your source into a collection, then use the Gallery to render the collection. You can then remove/add/edit items from the collection and this would be reflected in the Gallery, however without affecting the source.
Please be aware that Collecting data is limited to 500 rows at a time, (or 2000 with preview settings enabled) so you may want to filter your data to make it more relevant. Even Galleries connected directly to source only render 500 rows at a time (they fetch 500 at a time as you scroll through the data), but with filtering sources you need to take delegation into account.
To collect data;
Collect(myCollectionName, source)
where myCollectionName is a name you give your collection and source is the name of the custom connector source you've added to your app. There is no Filter applied to this formula, so it will simply return the first 500 rows of data.
You can then create a Gallery and set it's Items property to myCollectionName
From here, you can decide how best to facilitate removing data from your collected copy rendered in the Gallery - if you want to do it one-by-one in the gallery, then edit the first card of the gallery and insert something like a trashcan icon. It should appear on each row of the gallery if you're adding it to the right place. You can then set its OnSelect property to
Remove(myCollectionName, ThisItem)
If you prefer to have one delete button somewhere on your screen, you can just add a button, change the button text to "Delete" and then set it's OnSelect property to
Remove(myCollectionName, GalleryName.Selected)
where GalleryName is the name of your Gallery. This will delete the currently selected item in the gallery.
Hope this helps,
RT