To boot leader of government out of Lagos, a new order's required (4)

I believe the answer is:

also

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'to boot' is the definition.
('to boot' means also or in addition)

I don't understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for also that I've seen before include "As well, in addition" , "an indication of more to come" , "in accompaniment" , "Likewise" , "What's more" .)

I've seen this clue in The Times.

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