Use the time pressure inherently baked into your internship: Keep in mind the amount of days you have left until your mid-cycle review and final review. If you want to make it more concrete, add a countdown to your computer or track it physically with a calendar.
Leverage social pressures: If you can, go into the office. It's awkward to watch a YouTube video in front of your hard-working coworkers; this environment will make you want to be super productivity. If you can't go into the office, try virtual coworking, which is just a bunch of engineers hanging out passively on a video call. This is something I did among the Robinhood Android team.
Have a daily goal: After defining it, make it more concrete by adding it somewhere to your computer or having a physical sticky note. Adhering to this the first couple times will be the hardest: After you get into the rhythm, your brain will register it as a habit and will just naturally want to achieve something every day!