Wants to enter a training scheme
Can you assist me please? , I would like to apply as a trainee in my career job within the organisation that I am currently employed by.
Please advise me how to go about it and offer me any tips, please, they will be of great help too.
Your assistance will highly be appreciated.

Speak to your line manager first of all. Get their buy in, approval and advice. It may be that if you are accepted on a training programme they will need to replace you, so give them time to think about that.
In many companies they will ask your line manager for a reference for you, and a release date, and so you will need them to be willing to let you go.
Ideally you want them to speak well of you, and not be back footed when asked if /when they will release you. So make an ally of them in your cause.
Then depending on the company infrastructure you probably need to speak to HR, or maybe the head of the department you want to join. Or both.
You may have to wait for a vacancy to arise, and may have to go through a selection process along with other candidates.
Always worth making your ambitions known though. When I was in my twenties I was working for a large retailer as a merchandiser, but had ambitions to be a buyer. I waited, literally years, for a vacancy for a trainee buyer to be advertised.
I applied, along with hundreds of other people, went through the selection process and was given the position.
But the buying manager said to me afterwards “why didn’t you say you wanted to join the Buying Office? We would have made a position for you? “ .
So speak to your manager and take it from there.