If your account is a retirement account, such as an IRA, 401(k), 403(b), or pension plan, you can start the process of moving those over via the "Start a Rollover" button found on the Summary page of your Betterment account. Please note you must be logged in from a web browser to initiative a rollover.
For non-retirement accounts, such as taxable, brokerage, or money market accounts, you will need to sell your shares and redeposit the funds into your Betterment account as cash via a linked bank account in your name. As this typically results in tax consequences, you can see if you have any other losses from prior years or the current year in which you can use to offset your potential realized gains.
You can use our guide here to determine if moving over is right for you.
If the non-retirement account you are transferring contains whole shares of ETFs that match the ETFs in the Betterment portfolio, let us know, and we can provide you with instructions on how to move those assets over without having to liquidate.
See the "Parallel Security" section of our Tax Loss Harvesting White Paper for the complete list of ETFs within Betterment's portfolio.