Jimmy needs your help!
Python 2, 70 67 bytes



lambda s:S('/',' ',S("\S.{5}","----- ",s+' '*5))
import re;S=re.sub


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-3 bytes thanks to Kevin Cruijssen &amp; Neil

Not the prettiest, not sure how to better handle those leftover slashes...

Unfortunately, we can't replace both ends of each platform with spaces using a single re.sub call, because in the case of 2 platforms being one space apart, the gap between them can't be matched more than once. A lookahead/lookbehind assertion won't help, because anything matched within those assertions doesn't get replaced.

Using a single re.sub reference:

Python 3.8 (pre-release), 78 bytes

lambda s:[s:=re.sub(".[^/ -].{5}"," ----- ",s+"  ",1)for c in s][-1]
import re


Try it online!