Once you get in the water for a bit, you'll get used to it, so don't put any cold water in the bath.
Once you sit in the bath for a minute or so it will feel just right.
ーOnce you get in the water for a bit, you'll get used to it, so don't put any cold water in the bath.
「少し入ったら慣れるよ。だから水を足さないで。」
once you get in 「一度・一旦入ったら」
get used to ... 「…に慣れる」
put ... in ... 「…に…を入れる」
ーOnce you sit in the bath for a minute or so it will feel just right.
「数分お風呂に使ったら、ちょうどよく感じるよ。」
sit in the bath で「お風呂につかる」
feel just right で「ちょうどよく感じる」
ご参考まで!