Custom Check for customer fields

I have created a custom field for sales master data.

The need is to check if the input field is correct (correspond to a value of the table)

It seem's it can be done with the custom Validate Customer Badi. But it's not allowed to do a select on the table ZZ1_F19F..... I've tried to add a class in Custom Reusable Elements but I can't access directly to the table ZZ1_F19F.... neither if I create a CDS for this table

Do you have any idea for this requirement ?