你可以说"I'll take a shower first."
这句话的来源："shower"是英语中表示淋浴的词，而"take a shower"则是指洗澡的意思。
以下是一些例句：
I'm going to take a shower before I go to bed.
(我要先洗个澡再睡觉。)
Can you please let me know when dinner is ready? I'll take a shower in the meantime.
(晚饭准备好后请告诉我，与此同时我要先洗个澡。)