Short answer: If you didn’t swallow anything, your upvās is generally still valid.

A little detail, kept simple:

• If it did not go past the throat (you spat it out right away): In both Śvetāmbara and Digambara practice, the fast is usually not considered broken. Rinse your mouth with boiled water (within your allowed time), do a brief ālochana/pratikraman for the carelessness (pramāda), and continue.
• If even a small amount actually went down the throat:

- Śvetāmbara view: If it was food (not just allowed boiled water) and it crossed the throat, the upvās is typically counted as broken. Do ālochana/pratikraman and you may keep the rest of the day on boiled water as a self‑discipline, then retake the vow properly another day. - Digambara view: Accidental swallowing also breaks the anśan (fast). Do prāyaścitta according to your capacity, keep the day with greater vigilance (e.g., only boiled water if that is your niyam), and undertake upvās again on another day.

In all cases, intention matters morally, but the rule of “crossing the throat” decides the technical status of the fast. If you’re unsure what exactly happened, renew your pachchakkhāṇ/niyam and observe extra care for the remainder of the day.