All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger.
The substance in reference (silicone gel) may be used for prohibited purposes such as exaggerated improvements of one's appearance, and it may also be used for lawful purposes such as the removal of a deformity or to mend a physical defect, and there is no harm in that, as underlined in fataawa 88193, 87248 and 86061. There is no harm in manufacturing and selling this substance as long as one knows that the person who orders it would most likely not use it for a prohibited purpose.
In any case, there is no harm in working in this company, even if you partake in manufacturing this substance. However, if you know or believe that the entity buying this substance will most likely use it for a prohibited purpose, then you must not help them in this regard; Allaah, The Exalted, says (what means): {And cooperate in righteousness and piety, but do not cooperate in sin and aggression.} [Quran 5:2]
Allaah knows best.