Updating checkbox field in an automation

Hi guys,

I have the following situation: I need to update the contents of a checkbox field in an automation.
This means: ticking for example one specific checkbox and leaving the others as they are.
With the automation action ‘Update contact field’ it seems only possible to update the whole field (and thus also overwriting the options that you don’t need to change)

I don’t see how I can do this without creating an automation that branches off to all possible variations in a checkbox field (which grows exponentially with the amount of options)

Any ideas?
Thanks!