NSDateFormatter returns nil for date 13 Jan 2020 05:22:03 -0800

I am trying to formate email dates but date formatter returns nil where last five characters -0800. Doesn't have any problem with date has +0000. I have list of mixed dates of emails ending with +0000 and -0800

How can I add that 8 hours difference to my date to make it +0000? Some emails have sent from LA date origin as 13 Jan 2020 05:22:03 -0800. But, I am accessing in UK with 8 hours difference.

13 Jan 2020 05:22:03 -0800 should look a like 13 Jan 2020 13:22:03 +0000

- (NSDate *) date
{
    NSString *d = [headers objectForKey:@"date"];
    if (d == NULL)
        return NULL;

    NSRange rng = [d rangeOfString:@" ("];
    if (rng.location != NSNotFound)
        d = [d substringToIndex:rng.location];

    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"en_GB"] autorelease]];
    formatter.timeZone = [NSTimeZone timeZoneForSecondsFromGMT:0];
    [formatter setDateFormat:@"EEE, dd MMM yyyy HH:mm:ss ZZ"];
    NSDate *result = [formatter dateFromString:d];
    [formatter release];

    return result;
}

13 Jan 2020 05:22:03 -0800 is the specific date returns nil. Any help is appriciated.

I tried below statements

[formatter setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"en_US"] autorelease]];
[formatter setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"] autorelease]];
[formatter setLocale:[[[NSLocale alloc] initWithLocaleIdentifier:@"en_GB"] autorelease]];
[formatter setLocale:[[NSLocale currentLocale] autorelease]];

[formatter setDateFormat:@"EEE, dd MMM yyyy HH:mm:ss z"];
[formatter setDateFormat:@"EEE, dd MMM yyyy HH:mm:ss zz"];
[formatter setDateFormat:@"EEE, dd MMM yyyy HH:mm:ss zzzz"];

[formatter setDateFormat:@"EEE, dd MMM yyyy HH:mm:ss Z"];
[formatter setDateFormat:@"EEE, dd MMM yyyy HH:mm:ss ZZ"];
[formatter setDateFormat:@"EEE, dd MMM yyyy HH:mm:ss ZZZZ"];

The date string does not contain a weekday, so the specifier EEE is wrong anyway.

Set the locale to en_US_POSIX and use the format dd MMM yyyy HH:mm:ss Z

By the way there is a shorter and more convenient syntax

formatter.locale = [NSLocale localeWithLocaleIdentifier:@"en_US_POSIX"];           
formatter.dateFormat = @"dd MMM yyyy HH:mm:ss Z";

You can find the complete list of format specifiers on unicode.org