I'm assuming that row is a hash reference? If so then all you need to do is:

$row->{tjeneste_type} = $tjeneste_type;
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That adds a new key to your hash reference and enters its value.

Also you might be able to simplify things by not using an array reference at all. DBI has a nifty little method fetchrow_hashref which as the name implies automatically gives you a hash reference with the field names as keys.

Of course all this is assuming that's what $row is. :)