The difference between Do up and Undo

When used as verbs, do up means to fasten (a piece of clothing, etc.), whereas undo means to reverse the effects of an action.

Undo is also noun with the meaning: an operation that reverses a previous action.

check bellow for the other definitions of Do up and Undo

Do up as a verb (transitive, idiomatic):

To fasten (a piece of clothing, etc.); to tighten (a nut etc.)

Examples:

"I can't do up my shirt. The button is missing."

"Help me do up this zipper."

"You hold it in place while I do up the nut."
Do up as a verb (transitive, idiomatic, colloquial):

To redecorate (a room, etc.).

Examples:

"I'm going to do up the living room next."

"They've done up the house so that they can sell it more easily."
Do up as a verb (transitive, idiomatic, informal):

To execute a task or performance.

Examples:

"This time I'm going to do it up right."
Do up as a verb (transitive, idiomatic):

To pack together and envelop; to pack up.

Examples:

"I did up the parcel with string and took it to the post office."
Do up as a verb (transitive, dated):

To accomplish thoroughly.
Do up as a verb (transitive, archaic):

To starch and iron.
Do up as a verb (slang):

To beat up; to physically assault.

Undo as a verb:

To reverse the effects of an action.

Examples:

"Fortunately, we can undo most of the damage to the system by the war."
Undo as a verb:

To unfasten.

Examples:

"Could you undo my buckle for me?"
Undo as a verb (figuratively):

To impoverish or ruin, as in reputation; to cause the downfall of.

Undo as a noun (computing):

An operation that reverses a previous action.

Examples:

"How many undos does this program support?"