Question: After Yirmiyah brought them back, they only remained in the land for another thirty-six years, as Tosfos explained earlier in the second Perek (on Daf 12b)

Question (cont.): In that case, they did not remain there until the Yovel; so how can we find that "They listened and sent them away"?

Answer: It is possible with regard to Avadim that they had before they went into Galus (See Avodah Berurah).

Implied Question: And when the Gemara asked earlier 'Is it not written "And they heard and they sent away?"

Answer: The real question is from the Pasuk (Yirmiyah, 34) "And all the princes and all the people heard that they entered into the covenant" - implying that they entered into a covenant to send away their Avadim when the Yovel arrived.