Remember that the days of the Jewish calendar went from sunset to sunset—not midnight to midnight. So sometime during the daytime of Tuesday, Nisan 13th, Jesus' disciples prepared for them to eat their Passover meal.
When the evening came, after 6 pm of Tuesday, Nisan 13th, it became the Wednesday, 14th of Nisan.
The Word of God then says in Matthew 26:20–21,
“Now when the evening was come", (after 6 pm of Tuesday, Nisan 13th, when it became the Wednesday, 14th of Nisan)
"He sat down with the twelve. And as they did eat….”
and in Mark 14:17–18,
“And in the evening" (after 6 pm of Tuesday, Nisan 13th, when it became the Wednesday, 14th of Nisan)
"He cometh with the twelve. And as they sat and did eat….”
and in Luke 22:14,
“And when the hour was come" (after 6 pm of Tuesday, Nisan 13th, when it became the Wednesday, 14th of Nisan),
"He sat down, and the twelve apostles with Him.”
When the evening came, it became Wednesday, the 14th of Nisan. So Jesus and His disciples then ate the Passover meal.
Therefore, the disciples prepared for all of them to eat their Passover meal—including the killing of their Passover lamb—during the daytime of Tuesday, Nisan 13th.
The disciples came to Jesus asking Him where to prepare the Passover meal on the first day of the days of unleavened bread, Tuesday, Nisan 13th.
They were not asking Him where to prepare the meal on Thursday, Nisan 15th, the first day of the feast—after the Day of Passover, Wednesday, Nison 14th and the celebratory meal were over!
Again, Some of the confusion arises because many Christians do not understand the Old Testament Jewish calendar. They don't understand the difference between the Day of Passover for The ACTUAL Feast of Passover (also known as the Feast of Unleavened Bread, THE ANNUAL SABBATH HIGH DAY, THURSDAY, Nisan 15th) when the Passover meal was eaten on the 14th of Nisan on Wednesday,
and the Feast of Passover The ACTUAL Feast of Passover (also known as the Feast of Unleavened Bread, THE ANNUAL SABBATH HIGH DAY, THURSDAY, Nisan 15th) which ran for seven days from the 15th of Nisan through the 21st of Nisan.
They also do not understand that the “days of unleavened bread” began the day before Passover, on Tuesday, Nisan 13th.
So, the “Feast of Unleavened Bread” is NOT the same as the “days of unleavened bread.”
The “Feast of Unleavened Bread” (Thursday, Nison 15th through 21st) (BEGAN ON The ACTUAL Feast of Passover (also known as the The Feast Unleavened Bread, THE ANNUAL SABBATH HIGH DAY, THURSDAY, Nisan 15th) and The “Feast of Unleavened Bread” (Thursday, Nison 15th through 21st) is only the last seven days of the “days of unleavened bread” (Nisan 13th through 21st), below;
The “days of unleavened bread” were the 13th day through the 21st day of the first month on the Jewish calendar (Abib or Tuesday, Nisan 13th through Wednesday, 21st).