If you haven't yet been Accepted into the 506(c) offering, you may contact the company you're investing in to request a refund/cancellation.
If you've already been Accepted into the 506(c) offering, the ability to cancel your investment may depend on whether or not your securities have been issued. It is also recommended to contact the company you've invested in, in this scenario.
Once you have funded and been countersigned by the company, you will need to contact them directly for anything surrounding changes to the investment, as securities may have already been issued to you. If securities have been issued, it is a more involved and costly process for a company to refund you and cancel them.