Usage of Present Perfect Tense



Hello, and thank you for your question.
When using the Present Perfect, there will always be the words 'have/haven't' or 'has/hasn't', and then you will use the Past Participle form of the verb. In the example that you mention, the Past Participle verb is 'finished'. So it will look as follows:
"They have finished their project already."
A good suggestion would be to learn the Past Participle forms of verbs in order to correctly form the Present Perfect tense.
I hope that this example helps you. Please reach out if you have any further questions.