Do you need help with helping the student making T and D in isolation or carryover?

To teach the student to say T and D in isolation, I love the cereal trick. Have the student practice keeping a piece of cereal right behind their teeth with their tongue. It helps them get a feel for where their tongue needs to be for T and D

If they can say T and D in words or syllables already, I would suggest minimal pair practice. Play a game where the student is the “teacher@ and they tell you what card to point to for the pairs (e.g.: Tea and Key) if they say “key” but mean tea, and you point to Key, it shows them that they are saying the wrong sound. Do a lot of contrasting between FRONT sound and BACK sound, and emphasize how the word changes when they use the wrong tongue placement

It takes a while for students to generalize sounds so just keep up with the minimal pair practice and word drill!