Hi @Ny
You apply for the new permit 16g with your local Ausländerbehörde.
Until this new law for the residence permit 16g was brought in, a person who had a Duldung and found an Ausbildung could only receive the temporary status of 'Ausbildungsduldung'. Now there is the option for such a person to get either the Ausbildungsduldung or the permit 16g.
The main differences are that to get 16g, a person's identity must be verified (ideally with a passport) and they must be financially secure. If a person is doing a 'duale Ausbildung', they are allowed to access the money from BAB (Berufsausbildungsbeihilfe) in order to finance thie Ausbildung.
Best,
Éanna