Minh is the last boy who leaves the boat.

Minh is the last boy who leaves the boat.

=> Minh is the last boy to leave the boat.

‘The last’ refers to a single person. So to shorten the relative clause, we omit the relative pronoun and then change the verb or auxiliary verb (if any) into to + Verb (to infinitive) form.

Translation: Minh was the last guy to leave the boat.