thank you for sharing your question with the Wefugees community.
You can change your apprenticeship, but it is very important to comply with the correct order.
If you apply for changing your apprenticeship, the current apprenticeship will and automatically and you will lose your residence permit.
So you should pursue your current apprenticeship and try to get the new contract in the meantime. When you obtain it, you send it to the immigration office and apply for a new "Ausbildungsduldung". You have to stay in your cuurent apprenticeship until you receive the new permit and give notice to your current employer only then. Also take care of the notice periods which are written in your contract.
Another important point: You have to make sure that the beginning of your new contract is the beginning of your new vocational training, that is, that you're also registered in the vocational training school by then. As you already mentioned, vocational training normally starts in September. If the new employer wants you to start earlier, make sure that these months before September aren't just a kind of internship.
I hope my answers were helpful and I’ll be very pleased if you contact me again with further questions. I'm a consultant with mbeon and I‘ll be glad to guide you over a longer period of time. mbeon is an online advisory service for migrants via app, which you can download on your smartphone for free. You'll find me in the mbeon-app under my name „München, Frau Müller“ and get confidential one-to-one advice in a safe virtual room where nobody can read messages. For further information please visit www.mbeon.de.