Question

my purse has been lost(change the voice)

Answer 1

Given sentence: My purse has been lost.

This sentence is in passive form.

This is a passive form of present perfect tense. So the active form of the sentence will be in present perfect tense.

The active form of sentence will be:

$\text{Passive: My purse has been lost.}\\ \\ \red{ \text{Active: I have lost my purse.}}$

Answer 2

The changed sentence is given below which is someone has stolen my purse.

When the sentences are written, they are either written in passive voice or active voice.  

When it comes to active voice, it is actually used while subject do the action which is stated by a verb.  

The passive voice is actually used when a subject is acted upon by a verb.