I don't believe there's any custom date and time format string which will parse or format a time zone abbreviation. You'll have to strip it out, parse the local part, work out which time zone is meant from the abbreviation (good luck with that - they're ambiguous) and then apply that time zone to the local time to get a UTC value (again, this can be ambiguous).
If you're in control of the format at all, I would try to avoid including time zone information if you can, or include an offset rather than a time zone if that's all that's important (an offset doesn't give the same information of course), or an unambiguous time zone identifier if you really need the time zone. Note that .NET uses the Windows system time zone identifiers; my own Noda Time project uses the more widespread Olson / zoneinfo / tz identifiers, if that's helpful to you.
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