You are looking at the action called change

change {thing1} to {thing2}

Changes an objects field to something else.

A thing describes an objects fields and you have to name them correctly like this the mouse's name.

Thing2 is usually a string of text "gilbert" or a number 123 however it can be another object's field.

To blank a field, change it to "nothing" eg:
create a frog called gilbert
change the frog's name to nothing

This is an advanced command which may cause untold damage if used incorrectly.
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