Statement
"If Mr 'X' does not mend his ways. I will call the police.
Assumptions
I. Mr. 'X' may mend his ways.
II. The police may help me.
III. Mr 'X' was my friend in past.

'It he does not mend his ways' implies that there is a possibility for him to mend his ways. Hence, Assumption I is implicit. Further, the person is depending upon the police, if he finds it necessary. It means the person must be assuming that police will help him. Hence, Assumption II is also implicit. Assumption III is nothing to do with the given statement.