Short answer: No. If you have already taken Upvās Pachchakkhan, you do not need to take a separate Chauvihār Pachchakkhan for that same period.

Why:

• Shwetāmbara tradition: Upvās means no food for the whole day, and after sunset even water is not taken. So the night’s Chauvihār (no food or water after sunset until sunrise) is automatically included in your Upvās vow.
• Digambara tradition: Upavāsa is typically stricter (often nirjala). Chauvihār is naturally covered within this stronger fast.

When you might still say Chauvihār Pachchakkhan:

• If your local maryādā is to reaffirm Chauvihār at sunset during evening pratikraman, you may recite it as a respectful reinforcement, but it is not an additional requirement once Upvās Pachchakkhan is already taken.
• If you intend to alter the original vow (e.g., you had planned sajala upvās and now wish to extend/modify restrictions), then take a fresh, clear Pachchakkhan matching the new intent.

For simple, ready wordings of Pachchakkhan:

• Chovihār nu Pachchakkhan:
• Pachkhan for different taps (examples, including Chauvihār):

Follow your sect’s maryādā and your Guru’s guidance to keep the vow pure and exact.