For the Loading Screen Replacement:
Install at PAYDAY3/PAYDAY3/Content/Movies, copy BG_LoginVideo_01.bk2 and move it somewhere safe as a backup, then rename WednesdayIntro.bk2 to BG_LoginVideo_01.bk2.

For the Intro Screen Replacement:
Install at PAYDAY3/PAYDAY3/Content/Movies, copy StartUp_SBZ.bk2 and move it somewhere safe as a backup, then rename comfibeatshappy.bk2 to StartUp_SBZ.bk2.

For the StartUp With Audio Replacement:
Install at PAYDAY3/PAYDAY3/Content/Movies, copy StartUp_SBZ.bk2 and move it somewhere safe as a backup, then rename StartUpWednesdayIntroAudio.bk2 to StartUp_SBZ.