Hello Mariela,
If you mean that you already have the whole map and the whole structure open, you can use "volume zone" to show only the map near some specified atoms.

Example commands to show only map near residue 10 in chain B of model #1:

open 1a0m
hide ribbons
show atoms
open eds:1a0m
volume #2 level 0.8
volume zone #2 near #1/B:10 range 2.5

You can also do things with the GUI instead of commands although harder to explain with words in email.  For example, you can adjust the volume contour level with the slider in Volume Viewer,  you can select the atom(s) you want with the mouse (Ctrl-click, Shift-Ctrl-click),  and then just click the icon in the Map section of the toolbar across the top of the window to show the zone near the currently selected atoms.

How the icon looks is shown in the help for "volume zone" command:
<https://rbvi.ucsf.edu/chimerax/docs/user/commands/volume.html#zone>

To turn off the zone and go back to the whole map:

volume unzone #2

Not all PDB files have a 2fo-fc map in the EDS.  If you don't have the map, I don't know how you could get it -- maybe somebody else has the answer for that.

I hope this helps,
Elaine
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Elaine C. Meng, Ph.D.                     
UCSF Chimera(X) team
Resource for Biocomputing, Visualization, and Informatics
Department of Pharmaceutical Chemistry
University of California, San Francisco