Hi,
I don't know how to do it from ChimeraX, but if you open the cif or pdb file in a text editor and compare with a file from the PDB, you could figure out where and how this info is written and then write it manually in your file.
If this is a file you are going to deposit to the PDB, the deposition process will collect all the necessary info from the form and generate a cif file with it, so in the end the cif file after deposition and release will contain all the info that your pre-deposition
file did not have.
Guillaume