The Chinese solar calendar (which BaZi uses) doesn't have leap months — that's a lunar calendar feature. BaZi months are based on the 24 solar terms (节气), which divide the solar year precisely and don't require leap adjustments.
So a birth in a lunar leap month still falls within a specific solar term, and that solar term determines the Month Pillar. The leap month itself doesn't create a special BaZi rule.
If you're born during a lunar leap month, simply use your Gregorian birth date for the chart calculation. The system will place you in the correct solar term automatically. There's no need for manual adjustment.