Most effective way to clean data?

Hi,

I've recently started transfering data from the CRM into Power BI and it literally brought in everything. There are 500+ tables that have been transfered. I'm playing around with a table that I will be using quite frequently but it's got 498 columns and most of that is full of null values.

Is there a more effective way of clensing the data or do I need to manually delete 470 columns?

Thanks