Hello plum, 妳可以说：我要怎麽付给你？

It depends on the context. If someone helped you and you want to pay him/her back, you can say “我要怎么回报你呢?”. If you owe money to someone and you are not sure if he/she wants cash（现金）or online transfer（eg.支付宝/微信转账）, you can say”我要怎么给（付）你钱呢？”. Chinese people rarely use check in their daily life lol.

我怎么付你？