The Mujaheddin did need help, they needed weapons, bombs, intelligence, diplomatic support, booby traps specifically procured by the CIA. The US provided it.

And then back home, they used their contacts in the media to make sure everyone knew that the Mujaheddin were the good guys worthy of America’s support, even if they were not officially receiving it. Americans, Mujaheddin, and Soviets all understood the US supported the Mujaheddin, even if there was a layer of plausible deniability. It’s why the Soviets asked the US to stop the attacks on Soviet soldiers during the pullout and not Pakistan.

The american people were told to see the Mujaheddin as their ally, and the Mujaheddin understood it was the US supporting them.