The option to opt out of the hustler fund is currently not available on all network service providers (Safaricom, Telkom, and Airtel).
This means, as of the day of publishing this answer, once you opt-in to the hustler fund, there is no option to opt-out.
This is a feature that has been requested by many Hustler Fund users who either want to change their phone numbers or did not receive a loan after registration and therefore want to leave.
We will update this answer once the opt out of hustler fund option is added on USSD.