Create trigger to get ID of the foreign Key

[Harold Content]

I found out that a trigger can be helpfull to do action on inserting a new row.
An product has a brand when inserting i need the primairy key(id number) form the brand name to to put in the record for the product.

What would be a trigger that helps to get the id form the brand

1 Brand A
2 Brand B
3 Brand C


Example
Toy1,1,pcs,Brand A


for the product table i need:

Toy1,1,pcs,1