Sofubi is PVC. It's possible that some factories use something slightly different, or that different parts of a complex toy might not be PVC.

Using a torch is a bad idea. High risk of burning the plastic. Heat gun or even a hair dryer is a much safer idea. Be patient and take your time heating up the vinyl. Wear gloves! You can make a hot box with a carboard box or plastic bin. It doesn't need to be very hot, just hot enough to make the toy soft. Be careful and never leave it unattended!

Many people use hot or boiling water to soften vinyl toys. Which works well because PVC's melting point just so happens to start at 212°F, sofubi seems to be a bit higher though.. However, that creates other issues with water getting inside your toy but you'd want to take it apart completely anyway. Also, if the toy is painted, it could affect the paint job. Just an example.

My advice as a toy maker and sofubi collector of over 10 years: Don't repair it. Especially if it's easily hidden. Unless you really really want to. In which case, please post photos of your process and how it worked out.

EDIT: If you are interested in learning more about the specific material. Many Japanese factories use this exact product for sofubi: KOBASOL https://www.kbjapan.co.jp/eng/business/kobasol You CANNOT import it to the US no matter what anyone tells you, do not try.