Add continuous numbers to each row if it doesn't contains specific string

The variable need to add continuous numbers to each row if it doesn't contain a specific string.
Here's the example:
I have some variables like this:

I want to add numbers to each row if it isn't "_". The output should look like this:

" _ " could appear in any position, not only at the start or end. And, the first row is not always " _ ".
I have no clue to do this. That would be very nice If anyone could guide me. Thanks!


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