If reverse works and not forward, the problem likely lies in the forward items.
It is common enough for the forward band to snap, You can confirm this by putting the shifter into 1. By putting the selector into 1st or 2nd we engage the manual 1-2 band in addition to the forward band. If the trans tries to move the car forward with slippage in 1st, then the forward band has broken.
Unfortunately to swap that out, you are in the neighborhood of a rebuild because it'* one of the first things in the assembly process.