Which hook to use

I want to edit some lines and add some stuff in learnpress/inc/emails/class-lp-email-finished-course-user.php in inc folder without changing main php files as I will lose all the edits on the plugin update , I want to change the last part of the file related to sending and trigger email , so that I put an if condition in that part which hook shall I use and where to place the code? Please advice with details, Thanks