Hi Susan,
you would say, "Il faut qu'il aille chez le docteur."
-- Chris (not a native speaker).
Bonjour Susan !
Here's a link to our lesson on chez to complete Chris's answer :)
https://progress.lawlessfrench.com/revision/grammar/how-to-say-at-someones-place-chez-prepositions
Bonne journée !
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