I have two tables

tablle - bm
id SERIAL PK,
est_nom INT,
nom VARCHAR(70)
CONSTRAINT FK_bm_est FOREIGN KEY(est_nom) REFERENCES est(est_id) ON DELETE SET NULL

table - est
est_id SERIAL PK,
est_nom VARCHAR(70)

i want to insert this data in bm
INSERT INTO bm
VALUES
(netx serial,'DAPR','leopold stotch'),
(netx serial,'LDGA','fredderik gauss'),
(netx serial,'SDCD','edward gortz')

but in column 2, est. They are not int.
I want to look for those values in the est table in the est_nom column and if it finds it, give me its est_id. and insert it in bm.est_id And if it doesn't find it, insert that data in the est table in the est_nom column and assign it a consecutive serial number. Then now I inserted it into bm with its new serial number.