How to stop my dog going to the toilet inside get my dog to understand that he has to do his business outside?

Take it out when it has eaten, slept or played. Stay out until he/she has had a wee. Praise him/her.
Set the alarm clock so that it is you waking your puppy up to take it out. That has a nice side effect that it will learn to wait for you in the mornings and not get impatient.
If an accident happens inside, just ignore it and make a note to yourself that you have to be quicker to take the puppy out next time.

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