Which sentence needs to be edited for pronoun agreement. A bicyclist uses their legs to power their bike. or A monkey can move from tree to tree by swinging with its legs and tail?

The sentence, "A bicyclist uses their legs to power their bike." is not incorrect based on the fact that the bicyclist is a general Word for any bicyclist, not identified as a male or a female. It is appropriate to use the plural, non-gender specific pronoun for a singular person in general.

You can edit the sentence to read:

"A bicyclist uses his legs to power his bike."

Or:

"A bicyclist uses her legs to power her bike."

The sentence, "A monkey can move from tree to tree by swinging with its legs and tail." also uses a correct pronoun antecedent agreement.