How to downgrade the version that mathes to Mathlib4

Stream: mathlib4

[Yahoo]

My lean version is 4.21. Due to work needs, I need to downgrade the lean version to 4.17, and mathlib4 must also be adapted to it. How should I do this?

[Ruben Van de Velde]

You add rev = "v4.17.0" to the mathlib section of your lakefile.toml

[Ruben Van de Velde]

And run lake update