Hi, I just outline the process how I would start a refinement of the magnetic structure - I will point you to: https://conference.sns.gov/event/22/page/5 where you can find the lecture notes for magnetic structure refinement.

1. Get the cif structure file from the ICSD and use cif to pcr to get the structural input file.

2. Run a refinement on the data in the paramagnetic regime to get the scale factor and peak shape.

3. Use SaraH (http://fermat.chem.ucl.ac.uk/spaces/willsgroup/)

3a. do a symmetry analysis

3b. set up a refinement pcr

4. use the refinement pcr as second phase, keeping scale factor and shape parameters. Thus you only refine the magnetic moment amplitude in your magnetic data set.

This should get you started, since the magnetic structure is k=0 you might have problems to determine the magnetic moment size correctly.