Advice on transforming distributions

I have a variable which is bounded 0-10. I have the distribution of
this variable in a population sample prior and post a particular
intervention. Prior the data is highly skewed toward 10. I suspect
that the difference between prior and post scores is normally
distributed i.e. the magnitude of the effect of the intervention is not
dependent on the prior score. However, as the prior scores are bounded
and highly skewed I think this is masking/confounding this result. How
should I transform either the prior score or the change in scores to
see if I am right?

Many thanks

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