Clearing fields value on the form based on choice filed

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I've got following fields:
1. Choice field with connection to MS SQL table - name of the supplier.
2. Text fields like address, postal code filled based on the value chosen in choice field from point 1.
3. Another choice field with bank account numbers - another MS SQL table filter by ID value from choice field in point 1.

Two qestions:
1. By clicking 'x' in supplier name choice field I'd like to remove all values from text fields.
2. By clicking 'x' in supplier name choice fields or by changing the value in supplier name choice field I'd like to refresh Account number choice fields. Now the previous value stays and new one are just added.