Clear lookup field filter if many to many relationship has no records

Hello ,
I have a N:N relationship between Account entity and Country (custom entity).
On the task entity form, I have account and country lookup fields. I filtered the country lookup field based on the N:N relationship with account using lookup Related Records Filtering option.
I would like to clear the lookup filter if the N:N relationship has no records.In other words, if the account is not associated to any country the country lookup field should display all countries.

Please advise.

Best Regards,

Eman Abed AlWahhab