When you're potty training your toddler and you want to get them to tell you they have to potty.
Tell them that when they are needing to potty that they should tell you when they need to potty.
Some kids may be able to tell you and might tell you they need to potty while other kids may not.
There's really no way to force the issue of a toddler telling you they need to potty as some will and some won't.
But during the potty training stage set a timer and take them to the potty at those times when you think they need to potty.
Have them drink more water or other liquids so that they will need to pee more often.
If you see them about to poop in their diaper or pull up take them to the potty and remove their diaper or pull up and explain to them that they now need to use the toilet for poop and pee.
If the child is under 3 they may not be quite ready and if not just put the diaper back on and wait a few more months to try again.
There's no need to force the potty training issue until the child is nearing 4 years old.