The use of "it" versus "them" as pronouns has nothing to do with living or non-living subjects.
Use "them" for plural subjects and "it" for singular subjects.
There is a 16-digit code on your card. Please enter it into the box.
There is only one 16-digit code, which makes the subject singular, so you say "it," referring to the entire code.
There are four 4-digit chunks on your card. Please enter them into the box.
There are four chunks, which makes the subject plural, so you say "them," referring to all the chunks.