Keep.

2 Chronicles 35:1-19
Then Josiah celebrated the Passover to the LORD in Jerusalem, and the Passover lamb was slaughtered on the fourteenth day of the first month. . . .

as it is written.

Exodus 12:3-20
Tell the whole congregation of Israel that on the tenth day of this month, each man must select a lamb for his family, one per household. . . .

Leviticus 23:5-8
The Passover to the LORD begins at twilight on the fourteenth day of the first month. . . .

Numbers 9:2-5
"The Israelites are to observe the Passover at its appointed time. . . .

Numbers 28:16-25
The fourteenth day of the first month is the LORD's Passover. . . .

Deuteronomy 16:1-8
Observe the month of Abib and celebrate the Passover to the LORD your God, because in the month of Abib the LORD your God brought you out of Egypt by night. . . .