Hey @Nolan Lemuel Augustine hopefully I can address your issues.
Can MS reverse or delete the charges on my account considering that the Sub was used for training and certification?
You can request a refund through a billing support request ticket, but this is not a guarantee of getting refunded. Normally, refunds are issued due to a lack of availability, a miscalculation in the service offering, or a missed SLA target.
Please advise if a dummy/training Sub can be setup in the Portal to avoid this in future.
Various Learning path materials; see Exercise - Create a Windows virtual machine - Training | Microsoft Learn, will have a sandbox that you can use. This allows you run commands to complete training(s) on the learn platform. Not all units will have this sandbox, but this sandbox doesn't go against your personal subscription. You won't be charged for the resources as the environment is temporary and is disposed when you conclude the module.
Beyond that, when you attempting to learn Azure, what I would do is create the resources I need to in a separate resource group. I would try complete said module on the same day and at the conclusion, delete the entire resource group.