I understand it is DEM. By granular flow I meant no gas phase (RO_G=0.0). If it is not a granular flow (there is a gas phase), and you need to settle particles, you can run a granular flow simulation until particles settle. This will be much faster than settling particles along with a gas phase.
I am guessing you have zero particle at time=0 and you use a mass inlet to drop particles from the top. You can also seed particles in an Initial Condition region. They won’t be packed but this should be faster than using a mass inlet. Then use Getting particle data into csv files straight from mfix - #2 by jeff.dietiker to save particle_output.dat at the end of the run. Rename this file to particle_input.dat and use it for your new simulation.
In general, once you have the particles position, you can create a particle_input.dat using the format described in 8.4. Frequently Asked Questions — MFiX 20.4-dev documentation