Question

Change the present tense stem form of the verb to the third person singular "s" form of the verb. arrive

Answer 1

The verb would be arrives

Answer 2

If we need to put the verb "arrive" into the 3 er person singular in the present form, we would say: "arriveS"

e.g: He arrives at any times every day. She arrives in a red car in the morning. 

The inflictive -S makes reference to the 3p singular in present simple tense. 
this modification will only occur with the subject he/ she and I, in the present simple tense.