The best way to simulate recycling in En-ROADS is to moderately adjust the following sliders:
1. Buildings and Industry Energy Efficiency (less energy is used to produce new materials and goods)
2. Methane and Other, adjusting advanced settings of "Adoption of best practices for energy, industry, and waste (CH4, N2O, & F-gases)"
More extensive analysis is needed to understand the exact amount you should move the sliders to simulate these approaches. It is safe to assume that recycling and plastic reduction can only compensate for a small portion of the action represented by either of these two sliders.