Why is the lerp function not moving part2 too 0.75?

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Solution

You're trying to lerp part.CFrame to itself, which will always return part.CFrame. I think you were trying to lerp part2.CFrame instead of part.CFrame.

local part = workspace.P1
local part2 = workspace.P2

function PartChange()
    task.wait(5)
    part2.CFrame = part2.CFrame:Lerp(part.CFrame, 0.75)
end

PartChange()