Help, how does someone who has only ever bought even know when to sell?

I bought SBSW like 4 months ago (South African Gold/Palladium/metals mining company) because some guy on Reddit talked about it. It has 84% returns since September (my returns are slightly lower). When I look at the all time stock charts, it's approaching what it was after a huge dip after COVID. This was my first stock after building a foundation of ETFs, but I really don't know how to navigate whether to sell or not. What sort of information should I be sorting through to make a better educated guess? And obviously I already took too much influence from a random redditor to buy it, so your words may hold some weight, lol.