Selecting a range using a loop

Hi there,
I am creating a data exporter for one of my spreadsheets that will select a large amount of data so I can copy it elsewhere

I am trying to select a large range of data from multiple columns, however the data is in every two columns and then misses one E.G:

ABCDEFGHIJKL in the list to the left I would want to select columns AB,DE,GH etc.... until one of the cells contains a value (which is in a variable from an earlier part of the code)

this is what i have

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what is happening in the above code is it will select the correct cells in the first iteration but then in the second iteration it will not append the new selection to the old one so all I end up with is the cells that are selected in the last iteration of the above

Can anyone help?