Could you please go through the textbook more slowly?
Could we please take more time going through the textbook?
1) Could you please go through the textbook more slowly?
「もう少しゆっくりテキストを進めてもらえますか?」
2) Could we please take more time going through the textbook?
「テキストを進めるのにもう少し時間をかけてもらえますか?」
Could you please ...? や Could we please ...? で丁寧にお願いする言い方になります。
go through the textbook で「テキストを進める」
more slowly で「もう少しゆっくり」
take more time で「もう少し時間をかける」
ご参考になれば幸いです!