5 When the camp is to move, Aaron and his sons are to go in and take down the shielding curtain and put it over the ark of the covenant law.

Read Numbers 4:5 Using Other Translations

And when the camp setteth forward, Aaron shall come, and his sons, and they shall take down the covering vail, and cover the ark of testimony with it:
When the camp is to set out, Aaron and his sons shall go in and take down the veil of the screen and cover the ark of the testimony with it.
When the camp moves, Aaron and his sons must enter the Tabernacle first to take down the inner curtain and cover the Ark of the Covenant with it.