Some ideas that very quickly come to mind (I'm sure you can come up with much better):
1. Pair accountability: match up with a random person, each making sure their counterpart votes (e.g. similar to https://www.stickk.com).
2. Dashboard with people pledging to vote, with drip emails to keep registered users engaged, and gamified to increase "points" by how many unique number of people someone has brought on the platform.
3. Send-a-postcard (e.g. with lob.com) to friends that may be at risk for not voting. Not paid by any campaign/SuperPAC. Paid and sent-by someone they know.
You have to address the underlying issues in the system.
The main reason that people don't vote is because they don't think their vote matters. This could be because:
1. They don't like any candidate (can 2 parties really represent the intricate positions of 350 million people?). EXAMPLE: Biden or Trump? Both old, both talk nonsense, both corrupt - why vote?
2. Once elected, the officials tend to bend the rule to benefit themselves, their party, or their friends. Rule of law is a joke these days. EXAMPLE: many executive orders that go beyond specifying HOW to enforce a law, into blatantly ignoring it. Look at the executive order stating DOJ shouldn't target marijuana if it is "legal" in a state - the law firmly requires a tax stamp and this order blatantly ignores that. Going to the root of the issue, you could say that tax law is unconstitutional because they don't make revenue from it and the law only give Congress the power to tax "for the purpose of raising revenue".
3. Their vote is one of millions, so they think their voice is diluted. Or they see the surey results and think it is decided already.
4. They see the value of voting to be less than their other activities that day (job, hobbies, etc).