YOU SAID:

The other day I went to the shop to buy milk, and the guy at the till was wearing a cowboy hat

INTO JAPANESE

先日、牛乳を買いに店に行ったら、レジの男がカウボーイハットをかぶっていた

BACK INTO ENGLISH

The other day, when I went to the store to buy milk, the cashier was wearing a cowboy hat.

INTO JAPANESE

先日、牛乳を買いに店に行ったとき、レジの店員がカウボーイハットをかぶっていました。

BACK INTO ENGLISH

The other day, when I went to the store to buy milk, the cashier was wearing a cowboy hat.