In English, we use phrases like by myself or by yourself. To say the same thing in Chinese, just add 自己 (zìjǐ, oneself) before the verb!
你自己去，我不想去！
Nǐ zìjǐ qù, wǒ bùxiǎng qù!
Go by yourself. I don't want to go!
To say that you’re doing something alone, use 一个人 (yígèrén, alone) before the verb instead.
你想一个人住还是跟朋友一起住？
Nǐ xiǎng yígèrén zhù háishì gēn péngyǒu yīqǐ zhù?
Do you want to live alone or with friends?
Even though we wouldn’t normally combine oneself and alone in English, you can use 自己 (zìjǐ, oneself) and 一个人 (yígèrén, alone) in the same sentence in Chinese for a bit of emphasis.
她有时候自己一个人去旅游。
Tā yǒu shíhòu zìjǐ yígèrén qù lǚyóu.
She sometimes goes traveling alone by herself.
我喜欢自己一个人去买东西。
Wǒ xǐhuān zìjǐ yígèrén qù mǎi dōngxī.
I like to go shopping alone by myself.