" To fill in" here means to do the work of someone else or to take someone else's place in doing the work that they normally do.

” 这里的“填补” 意味着做别人的工作或代替别人做他们通常做的工作。

" To ring up" someone or " to ring someone up" is a phrasal verb meaning to take someone's money in exchange for something they are buying from you.

“To ring up” someone 或 “to ring someone up” 是一个短语动词， 意思是用某人的钱来换取他们从你这里购买的东西。