Answer:
The pronoun "their" should be replaced by "its"
Explanation:
The dog is singular subject; hence it should attract a singular subject/object.
Also, we want to show that the "owner" is the possessor of the "dog", so a possessive adjective is needed to give attribute to the noun, "owner".
Hence, The pronoun "their" should be replaced by "its" is the best option.
The sentence then becomes
The dog ran fast until its owner stopped it.
