As explained on
sabiasque.pt/seguranca-social-direta.html
you can access your personal bank account details on Direct Social Security service on
app.seg-social.pt/sso/login?service=http...pt%2Fptss%2Fcaslogin
("Recebimentos da Segurança Social > Alterar conta bancária"). If you don't have an account on that service, you can create one on "Efetuar Registo".
